# Shipping Boxes & Mailers Pick the container from the item: clothes go in a flexible mailer, small sturdy things in a padded mailer, flat prints in a rigid mailer, rolled prints in a tube, and anything fragile or heavy in a corrugated box. Buy boxes by inside dimensions, with room for cushioning, and by board grade for the packed weight. Oversized boxes cost postage. ## How it works A shipping container must survive carrier sorting machines and stop the item moving. Corrugated board, a wavy paper layer called the flute glued between flat liners, makes a box that resists crushing and puncture. Its strength is graded by the Edge Crush Test (stacking) or the burst test (puncture and tear), printed on a bottom flap. Mailers trade that protection for size and weight. A flexible envelope suits items that cannot be crushed or broken; a padded mailer adds bubble film or paper padding; a rigid mailer's stiff paperboard keeps flat items flat. Carriers bill the greater of actual weight and dimensional weight (cubic inches ÷ 139 at USPS and UPS daily rates, 166 at UPS retail), so the smallest container with room for cushioning usually ships cheapest. USPS gives a flexible, thin, even mailer the cheaper flat (large-envelope) price; boxes, rigid and lumpy mailers pay parcel prices. [1] [21] [15] [7] [9] [22] [19] [6] [12] | Family | What it is | Suits | |---|---|---| | Corrugated box | Slotted boxes with four flaps (RSC), die-cut mailer boxes with a lid, multi-depth boxes scored to cut down, long boxes, and moving boxes; dish and wardrobe moving boxes are double wall. | Anything fragile, dense, heavy or irregular; moving house. | | Flexible mailer | An unpadded envelope of polyethylene film or paper with a self-seal strip. | Clothes and other soft goods that cannot be crushed or broken. | | Padded mailer | A paper or plastic envelope lined with bubble film, embossed paper bubbles or shredded paper. | Small items that will not break but need protection from scuffs. | | Rigid flat mailer | A stiff paperboard envelope, not graded corrugated, that will not bend. | Prints, photos, certificates and other flat things that must arrive flat. | | Mailing tube | A fiberboard tube with end caps; carriers sort it with irregular parcels, off the main conveyors. | Rolled posters, plans and art prints. | ## How an expert narrows the choice ```mermaid timeline section 1 · Container type corrugated box : ask Board grade, Multi-depth scoring : skip Mailer material, Film thickness, Padding, Mails as a USPS flat, Return strip flexible mailer : ask Mailer material, Return strip : skip Board grade, Box style, Flute, Multi-depth scoring, Padding padded mailer : ask Mailer material, Return strip : skip Board grade, Box style, Flute, Multi-depth scoring rigid flat mailer : skip Mails as a USPS flat, Film thickness, Padding, Board grade, Flute, Mailer material, Box style mailing tube : skip Mails as a USPS flat, Mailer material, Padding, Film thickness, Board grade, Flute, Box style, Multi-depth scoring, Return strip section 2 · Inside dimensions Item's length, width and height, before padding? section 3 · Board grade Packed box under 30 lb, or heavier? section 4 · Mailer material paper : skip Film thickness ``` 1. **Container type.** Clothes, small sturdy things, flat or rolled prints, or fragile or heavy? The item decides the container family, and each family has its own facets: board grade only for boxes, film thickness only for plastic mailers. The answer removes every other family from the set. If corrugated box: ask Board grade, Multi-depth scoring; skip Mailer material, Film thickness, Padding, Mails as a USPS flat, Return strip. If flexible mailer: ask Mailer material, Return strip; skip Board grade, Box style, Flute, Multi-depth scoring, Padding. If padded mailer: ask Mailer material, Return strip; skip Board grade, Box style, Flute, Multi-depth scoring. If rigid flat mailer: skip Mails as a USPS flat, Film thickness, Padding, Board grade, Flute, Mailer material, Box style. If mailing tube: skip Mails as a USPS flat, Mailer material, Padding, Film thickness, Board grade, Flute, Box style, Multi-depth scoring, Return strip. Skip if already known: a query naming the container (poly mailer, bubble mailer, rigid mailer, tube, box), a query naming the item, such as t-shirts, prints or a lamp, a query saying moving boxes. 2. **Inside dimensions.** Item's length, width and height, before padding? Size cuts any format down to a handful of products, and it sets postage through dimensional weight. Experts size from the item outward: for a box, item plus at least 2 in of cushioning on every side. Skip if already known: an earlier answer giving the item's size, a query giving a box size such as 12 x 12 x 12. 3. **Board grade.** Packed box under 30 lb, or heavier? Only asked for boxes. The heavier answer removes 32 ECT and lighter single wall, and keeps 200# with a warning, since IoPP puts it at about 30 lb and Uline's UPS column at 40 lb. Skip if already known: a format answer other than corrugated box, a query naming a grade such as 32 ECT, 200# or double wall. 4. **Mailer material.** Paper mailer for the recycling bin, plastic, or either? Only asked for mailers. A paper answer removes every plastic and mixed mailer, and the answer decides whether film thickness matters at all. If paper: skip Film thickness. Skip if already known: a format answer of corrugated box, rigid flat mailer or mailing tube, a stated preference for plastic-free or recyclable packaging. ## What to surface ### Container type The kind of container: a flexible mailer, a padded mailer, a rigid flat mailer, a mailing tube or a corrugated box. It sets the protection ceiling and the postage class. IoPP allows bags and padded bags only for easy loads, items not readily damaged by puncture or shock, and wants a box for fragile or dense items. USPS gives flat prices only to flexible, evenly thick mailers. Answers map: clothes to flexible mailer; small sturdy things to padded mailer; flat prints to rigid flat mailer; rolled prints to mailing tube; fragile or heavy to corrugated box. [1] [6] [7] [10] [19] Values: flexible mailer, padded mailer, rigid flat mailer, mailing tube, corrugated box. Question to ask: Clothes, small sturdy things, flat or rolled prints, or fragile or heavy? Used as: top-level split, filter. Data: derived from listing fields, backfill cost low. Look for it as: Not a field. Derive from title words: poly mailer, bubble or padded mailer, rigid or stay-flat mailer, mailing tube, box or carton. Title keywords settle almost every listing. Kraft fold-over book mailers made of corrugated go to corrugated box. Out of scope: unpadded, unstiffened letter and catalog envelopes (cards), boxes sold for storage rather than shipping or moving (storage-containers), and gift boxes not sold for shipping (gift-bags). ### Mailer material What the mailer is made of: paper only, polyethylene plastic only, or a paper outside with a plastic bubble lining. It decides how the recipient gets rid of it. Paper mailers go in curbside recycling with paper. Plastic film is not accepted curbside in most of the US; a plastic mailer goes to store drop-off, and only once its paper label is removed. A paper mailer lined with plastic bubbles fits neither stream. Answers map: paper for the bin to paper; plastic to plastic (polyethylene); either to no filter. [3] [4] [20] [19] Values: paper, plastic (polyethylene), paper outside, plastic bubble inside. Question to ask: Paper mailer for the recycling bin, plastic, or either? Used as: top-level split, filter. Data: derived from listing fields, backfill cost low. Look for it as: Title and first bullet: poly, kraft, paper, 'curbside recyclable', 'recyclable at store drop-off'. A kraft bubble mailer is the mixed value. Title words settle most listings. A kraft-outside bubble mailer is mixed unless the brand says the padding is paper. ### Inside dimensions The usable space inside: length × width × height for a box, with length and width at the opening and height to the base; width × length for a mailer, which has no fixed height. Box makers specify boxes by inside dimensions. Experts size a box to the item plus at least 2 in of cushioning on every side, the figure IoPP and FedEx's packing guide both give, then stop, since every extra inch adds dimensional weight. Answers map: for a box, each item dimension plus 4 in is the minimum inside size. For mailers the register filters on width and length and leaves the fit allowance to the buyer. [2] [21] [15] [1] [13] [11] Question to ask: Item's length, width and height, before padding? Used as: top-level split, filter, sortable. Data: on the listing, backfill cost low. Look for it as: The number is in nearly every title ('12 x 12 x 12'); brand tables label it 'INSIDE DIMENSIONS L x W x H' (Uline). Whether it is the inside or the outside is a separate facet, dimensions_basis. Parse the numbers from the title or spec table: three for a box or tube, two for a mailer. Do not adjust them for basis here. Chart: Box-in-box fit. ### Board grade The certified strength of the corrugated board, given as an Edge Crush Test value (such as 32 ECT) or a burst test rating (such as 200#), with single or double wall. The certificate's limit is for truck freight: 32 ECT or 200# board is certified to 65 lb, but IoPP keeps average and difficult parcel loads in it to about 30 lb. Uline's UPS column agrees for 32 ECT and allows 200# to 40 lb. Heavier parcels need 275# or double wall. Answers map: under 30 lb to 32 ECT, 200# or stronger; heavier removes 32 ECT and below and flags 200#. [1] [15] [6] [21] Values: not stated, single wall, below 32 ECT or 200#, single wall, 32 ECT, single wall, 200#, single wall, stronger than 200# or 32 ECT, double wall. Question to ask: Packed box under 30 lb, or heavier? Used as: top-level split, filter, shown on the card. Data: needs research, backfill cost medium. Look for it as: Brand spec tables print '200 LB. TEST', '32 ECT' or '275# DW' in the table header or model row. The box maker's certificate is on a bottom flap and sometimes visible in a photo. Brand pages carry it for most stock boxes; marketplace multipacks often do not. Backfill the top N from brand pages or certificate photos; leave 'not stated' rather than infer from wall type. No cited source gives a parcel limit for board below 32 ECT or 200#. Chart: Box strength ladder. ### Return strip A second adhesive strip on a mailer, so the recipient can reseal it to send a return. For clothing sellers who take returns, it saves the customer finding new packaging. EcoEnclose lists it on its poly and bubble mailers alongside a tear strip for easy opening. [19] Question to ask: Will customers send returns back in the same mailer? Used as: filter, shown on the card. Data: derived from listing fields, backfill cost low. Look for it as: Bullets: 'dual adhesive', 'double seal', 'return ready', 'second adhesive strip'. Derive from bullet text; absent means unknown, not no. ### Box style How the box is cut and folded: a regular slotted container (RSC) with four flaps, a die-cut mailer box with a hinged lid, a full-overlap box, a long box, or a moving box. The RSC is the default, easy to fill and flat on every face. Die-cut mailer boxes are folder-style boxes, often in thin E or F flute chosen for printing, so they suit branded presentation. IoPP recommends a full-overlap box, whose top flaps overlap completely, for heavy loads, and warns against styles with uneven faces in parcel sorting. [2] [21] [1] [18] Values: regular slotted (RSC), die-cut mailer box, full overlap (FOL), long box, moving box. Used as: shown on the card, filter. Data: derived from listing fields, backfill cost low. Look for it as: Title words: 'mailer box', 'tuck top', 'long box', 'moving box', 'FOL'. Derive from title words. Where a title says only 'shipping box' or 'corrugated box', default to RSC; that default is our heuristic, not a sourced rule. Checking the photo is research, for the top N only. ### Multi-depth scoring Whether the box or mailer is pre-creased at several heights so you can cut or fold it down to the contents. One multi-depth box stands in for several sizes, and cutting it down removes the empty space carriers bill as dimensional weight; Uline sells them for exactly that. Fold-over book mailers do the same with variable-depth scores. It matters to a seller shipping many item sizes from a small stock of boxes. [16] [17] Question to ask: Many different item sizes from one stock of boxes? Used as: filter, shown on the card. Data: derived from listing fields, backfill cost low. Look for it as: Title words 'multi-depth', 'adjustable height', 'variable depth', and a list of depths in the spec table. Derive from title and spec-table words; absent means unknown, not no. ### Padding What cushions a padded mailer: plastic bubble film, embossed paper bubbles, shredded paper between paper layers, or another cushion such as foam. It sets disposal and a little of the protection. Paper padding keeps a paper mailer curbside recyclable; an all-plastic bubble mailer can go to film drop-off; paper with bubble film inside goes to neither. Either way it is a bag: IoPP accepts padded bags to 20 lb for easy and average loads, and USPS sets 20 lb for reinforced or 70-pound paper bags. [23] [19] [20] [1] [6] Values: plastic bubble film, paper bubbles (embossed), shredded paper, other cushion. Used as: shown on the card, filter. Data: derived from listing fields, backfill cost low. Look for it as: Title or first bullet: 'bubble', 'paper padded', 'honeycomb', 'recycled newspaper fill'. Derive from title or first-bullet words; where they are silent, leave it unknown. ### Film thickness How thick a plastic mailer's film is, in mils (thousandths of an inch). Thicker film resists tears and punctures in sorting. IoPP's parcel guide sets floors for plastic bags carrying easy loads: at least 2 mil up to 5 lb and 4 mil up to 10 lb. USPS prints the same rule in millimetres, which we read as mil (see judgements). A thinner poly mailer suits light soft goods only. [1] [6] Used as: filter, shown on the card. Data: needs research, backfill cost medium. Look for it as: Brand pages and some titles give it as '2.5 mil'. Often absent on marketplace multipacks. Needs a brand-page lookup per product, since marketplace multipacks rarely carry it. Backfill the top N and leave the rest empty; do not infer thickness from the photo. Chart: position on a horizontal scale with the 2 mil and 4 mil floors drawn and labelled by load weight. ### Mails as a USPS flat Whether a filled mailer can go at USPS large-envelope (flat) prices instead of parcel prices. A flat must be at most 15 × 12 in and 3/4 in thick, flexible, rectangular and evenly thick; a rigid, lumpy or nonrectangular piece pays the package price instead, and First-Class flats stop at 13 oz. So only thin, soft contents in a flexible or thin padded mailer qualify; boxes, rigid mailers and tubes never do. [7] [8] [10] Used as: shown on the card, filter. Data: derived from listing fields, backfill cost low. Look for it as: Not a field. Derive from format and the listed size: no larger than 15 × 12 in, and a flexible or padded mailer. Compute at query time; thickness depends on the contents, so show it as 'can mail as a flat if under 3/4 in thick' rather than a promise. Chart: Flat-size template. ### Size basis Whether a listing's size gives the inside or the outside of the container, or does not say. Outside dimensions are larger by the board thickness on each wall, so a box listed by its outside is smaller inside than its number. Box makers quote inside dimensions, but carriers measure the outside for dimensional weight, so the basis changes both fit and postage. [15] [2] [21] [9] Values: inside, outside, not stated. Used as: shown on the card. Data: needs research, backfill cost medium. Look for it as: Brand spec tables print 'INSIDE DIMENSIONS' and 'Outside: 12 3/8 x 6 3/8 x 6 5/8' (Uline). Marketplace titles rarely say. Match the model to a brand page for the top N; otherwise record 'not stated' rather than guess. ### Flute The size of the wavy middle layer of corrugated board, lettered A, B, C, E or F. Flute sets wall thickness, cushioning and how well the board prints. C flute is the most common in shipping boxes; B shows up in fold-over book mailers; E and F are thin flutes used for printed mailer boxes. The letters follow the order the flutes were invented, not their size. [21] [15] [17] Values: A, B, C, E, F. Used as: shown on the card. Data: needs research, backfill cost low. Look for it as: Brand spec tables: 'MATERIAL: C flute', '200 lb. test, B-flute'. Rare on marketplace listings. Brand pages only; do not backfill beyond them. Not worth inferring. ## Numbers worth computing | Metric | Formula | Why | |---|---|---| | Billable weight (lb) | `max(packed_weight_lb, roundup(L × W × H × k / D)), outside dimensions in inches, each side rounded (USPS up, UPS to nearest); k = 0.785 for a nonrectangular parcel at USPS, else 1; D = 139 at USPS above 1,728 in³ and UPS daily rates, 166 at UPS retail; USPS charges at most the 70 lb price` | Carriers charge whichever is greater, so a light item in a box one size too big pays for air. It is the number that shows why multi-depth boxes and tight sizing save money. Outside dimensions come from the listing when dimensions_basis says outside; inside dimensions understate the result. [9] [12] [22] [15] | | Volume in cubic feet (cu ft) | `L × W × H / 1728, in inches` | USPS applies dimensional weight only above 1 cubic foot, so this says at a glance whether a box's USPS price follows its size or its weight. [9] | | Cushioning room per side (in) | `min((inside_L − item_L), (inside_W − item_W), (inside_H − item_H)) / 2` | IoPP and FedEx's packing guide both ask for at least 2 in between item and wall on every side; a box under 2 in per side is too tight for its cushioning. [1] [13] [6] | ## What you give up - A tighter box lowers dimensional weight, but it leaves less room for cushioning, and the packaging guides want a gap on every side. Size to the item plus cushioning, not to the item. [1] [9] [16] Board branch: "See more multi-depth boxes". - A mailer is smaller and lighter and may mail as a flat, but parcel guidance allows bags only for items that cannot be crushed or broken. Padding protects against scuffs, not drops. [1] [6] [7] Board branch: "See more boxes for fragile items". - ECT board is made to resist crushing in a stack; burst-grade board is made for tensile and tear strength, which IoPP says matters more in parcel handling. Uline's UPS guideline column rates 200# board above 32 ECT. [1] [15] Board branch: "See more burst-test boxes". - Paper mailers go in the household bin, but a life-cycle study cited by Wikipedia found a kraft mailer padded with newsprint had a higher overall impact than a plastic bubble mailer. [23] [3] ## How to draw it **Box strength ladder** (scale, shows Board grade). Puts each board grade on one scale with two weights: what the box certificate allows for freight and what parcel guidance allows. The gap between the two marks is the expert point. Used today by Uline prints this as a two-column table (Fibre Box Handbook versus UPS guidelines) on its box pages.. [15] [1] **Box-in-box fit** (other, shows Inside dimensions). Draws the item inside the box with the cushioning gap shaded, so a buyer sees at once whether the box is too tight or paying for air. This is a proposal, nobody draws it this way yet. **Flat-size template** (two axis map, shows Mails as a USPS flat, Inside dimensions). Plots mailers by length and width against the 15 × 12 in USPS flat rectangle, so it shows which ones can mail at flat prices. Used today by Proposal, from the USPS flat-size standard.. [7] ## Words you will meet - **Easy load**. IoPP's term for an item of moderate density that is not readily damaged by puncture or shock and does not shift in the package. - **Corrugated board**. Board made of a wavy paper layer glued between two flat paper sheets; what most people call cardboard. - **Flute**. The wavy middle layer of corrugated board, lettered A, B, C, E or F. - **Single wall, double wall**. Board with one wavy layer, or with two wavy layers and three flat sheets, which is stronger. - **Edge Crush Test (ECT)**. A lab test of how much load the board's edge takes before crushing, in pounds per inch; it predicts stacking strength. - **Burst test (200#, Mullen)**. A lab test of the pressure that ruptures the board, in pounds per square inch; it tracks puncture and tear strength. - **Box maker's certificate**. A stamp printed on a box's bottom flap giving the board grade, size limit and gross weight limit. - **RSC (regular slotted container)**. The standard box with four flaps top and bottom, all the same length, coded 0201 by FEFCO. - **FEFCO code**. The European box industry's numbering of box designs; it also fixes that box sizes are inside measurements. - **Inside dimensions**. The usable space in a box, length and width at the opening and height to the base. - **Dimensional weight**. A weight a carrier calculates from a parcel's size; you pay for it when it exceeds the real weight. - **Flat (large envelope)**. USPS's class for flexible, evenly thick mail up to 15 × 12 in and 3/4 in thick, priced below parcels. - **Poly mailer**. A flexible mailer made of polyethylene plastic film. - **Mil**. A thousandth of an inch, the unit for plastic film thickness. - **Store drop-off**. Collection bins at shops for plastic bags and film that household recycling does not take. - **Multi-depth box**. A box creased at several heights so you can cut it down to fit what is inside. ## Where we made a call - For parcels, rate a box by the carrier guideline weight, not the certificate limit, which is set for truck and rail freight. (confidence high). IoPP says the certificate is not a parcel-carrier requirement and keeps average and difficult loads in 32 ECT or 200# boxes to about 30 lb, against a 65 lb certificate. Uline prints both columns side by side. [1] [15] - For 200# single-wall boxes, IoPP's parcel limit is about 30 lb and Uline's UPS column gives 40 lb; we flag 200# between them. (confidence medium). Sources disagree. IoPP's 30 lb is for average and difficult loads and lets easy loads go heavier; Uline restates UPS guidance we could not read directly. USPS allows 200# board for soft goods to 45 lb. So a 30 to 40 lb parcel keeps 200# boxes, with a warning. [1] [15] [6] - Padded mailers are not for fragile items, although some brands sell them as ideal for fragile goods. (confidence medium). Sources disagree. EcoEnclose calls its newspaper-padded mailer ideal for fragile items. IoPP says bags should not be used for difficult loads, which include fragile objects. We side with IoPP, a packaging standards body without a product to sell. [19] [1] - USPS's plastic-bag floor reads 2 and 4 millimetres; IoPP's identical rule reads mil. We read USPS as mil. (confidence medium). Sources disagree. The two rules match word for word on load weights (5 and 10 lb). No poly mailer is 2 mm thick, about 79 mil, so the USPS unit looks like a misprint. Ours. [6] [1] - A paper mailer lined with plastic bubbles cannot be recycled curbside or at store drop-off. (confidence medium). EcoEnclose says so directly and says sorters reject paper mailers with hidden plastic padding. How2Recycle accepts only pure polyethylene film at drop-off, which rules out the paper outside. One seller and one label scheme. [20] [4] - IoPP asks for thicker mailing-tube walls than the USPS minimum at every tube length. (confidence high). Sources disagree. USPS sets the floor for acceptance; IoPP sets a performance target. Use IoPP's for anything valuable rolled; figures by length are in notes.md. [1] [6] - An unqualified 'recyclable' claim needs recycling access for at least 60 percent of consumers or communities; plastic mailers lack it curbside. (confidence high). The FTC's 60 percent counts consumers or communities; How2Recycle's Widely Recyclable label counts 60 percent of US recycling facilities, a different base. How2Recycle says film is not accepted in most curbside programs, so a poly mailer's claim must say store drop-off. [14] [5] [3] - The smallest box that fits the item plus cushioning is usually the cheapest to ship, because carriers bill dimensional weight. (confidence high). USPS and Wikipedia state the greater-of rule; Uline sells multi-depth boxes to cut dimensional weight. [9] [22] [16] - The dimensional-weight divisor is 139 at USPS above 1 cubic foot and at UPS daily rates; UPS retail rates use 166. (confidence medium). USPS is read from the current manual, revised July 2026; UPS from its own page (archived October 2025), which Wikipedia matches. FedEx is left out: Wikipedia's 139 cites 2017 pages, and FedEx's 2012 packing guide says 166. [9] [12] [22] - Corrugated loses much of its stacking strength in damp storage and under long-term load, so boxes left stacked after a move need a stronger grade. (confidence medium). IoPP gives the size of the loss (figures in notes.md); Wikipedia says long storage in high humidity calls for extra strength. Boxes sold for storage rather than moving belong to storage-containers. [1] [21] ## References 1. [IoPP Transport Packaging Committee, Guide to Packaging for Small Parcel Shipments (2002)](https://www.iopp.org/files/public/IoPPSmallParcelShippingGuidelines.pdf) (standards body). Supports: 32 ECT or 200# box certified to 65 lb for freight, about 30 lb for average and difficult parcel loads; certificate is not a parcel-carrier requirement; fill to about half its limit; bags not for difficult loads; padded bags to 20 lb; easy-load film 2 mil to 5 lb, 4 to 10; easy loads: moderate density, not readily damaged by puncture or shock; at least 2 in between contents and container walls for fulfillment packing; burst grade gives tear strength, ECT gives stacking; durability matters more for parcels; RSC for most items, full overlap for heavy loads, cushioning on all six sides; tube wall minimums by length; humidity and long storage cut stacking strength. 2. [FEFCO, International Fibreboard Case Code, 12th edition (2022)](https://www.fefco.org/sites/default/files/files/FEFCO%20Code_WEB%287%29.pdf) (standards body). Supports: box dimensions are internal: length and width at the opening, height to the base; slotted boxes (0200 series) versus one-piece folder boxes (0400 series). 3. [How2Recycle, Store Drop-off label](https://how2recycle.info/about-the-how2recycle-label/store-drop-off-us-only/) (standards body). Supports: plastic bags and films are not accepted in most US curbside programs; plastic mailers with a compatible label qualify for store drop-off. 4. [How2Recycle, Frequently asked questions](https://how2recycle.info/frequently-asked-questions/) (standards body). Supports: only pure polyethylene films go to store drop-off; plastic mailers recyclable at store drop-off only with the paper label removed. 5. [How2Recycle, Widely Recyclable label](https://how2recycle.info/about-the-how2recycle-label/widely-recyclable/) (standards body). Supports: Widely Recyclable means accepted by 60% of US recycling facilities. 6. [USPS Domestic Mail Manual 601, Mailability](https://pe.usps.com/text/dmm300/601.htm) (regulator). Supports: plastic bags at least 2 (to 5 lb) and 4 (to 10 lb), unit printed as millimeters; padded bags need a 60-pound exterior ply; 20 lb stated for reinforced or 70-pound bags; 200-pound board for soft goods from 20 to 45 lb; 275-pound board for heavy soft goods and parcels over 65 lb; box must leave space for cushioning; tube wall minimums by length. 7. [USPS Domestic Mail Manual 101, Physical Standards](https://pe.usps.com/text/dmm300/101.htm) (regulator). Supports: flats at most 15 x 12 x 3/4 in, flexible, rectangular, uniformly thick; boxes are not flats; rigid or nonrectangular pieces pay parcel prices; First-Class flats to 13 oz. 8. [USPS Domestic Mail Manual 201, Commercial Letters, Flats and Parcels](https://pe.usps.com/text/dmm300/201.htm) (regulator). Supports: flat limits 15 x 12 x 3/4 in on the commercial side; rigid or nonrectangular flat-size pieces are parcels. 9. [USPS Domestic Mail Manual 133 and 123, dimensional weight for Ground Advantage and Priority Mail](https://pe.usps.com/text/dmm300/133.htm) (regulator). Supports: dimensional weight applies above 1 cubic foot (1,728 cubic inches); round each side up, multiply, divide by 139, round up; greater of actual or dimensional; nonrectangular parcels multiplied by 0.785; dimensional weight above 70 lb pays the 70 lb price. 10. [USPS, Sending Letters and large envelopes](https://www.usps.com/ship/letters.htm) (regulator). Supports: rigid or lumpy large envelopes pay the package price; large envelopes priced up to 13 oz. 11. [USPS, Sending Packages](https://www.usps.com/ship/packages.htm) (regulator). Supports: dimensional weight may apply to your own packaging; use packaging with room for cushioning so items cannot shift. 12. [UPS, Shipping dimensions and weight (Internet Archive snapshot, 27 October 2025)](https://web.archive.org/web/20251027072758/https://www.ups.com/us/en/support/shipping-support/shipping-dimensions-weight.page) (other). Supports: dimensional weight = L × W × H ÷ divisor, sides rounded to the nearest inch, fractions up; divisor 139 for Daily Rates, 166 for Retail Rates. 13. [FedEx, How to Pack (2012 guide, Internet Archive snapshot 2015)](https://web.archive.org/web/20151123220911/http://www.fedex.com/us/services/pdf/How_To_Pack.pdf) (other). Supports: box-in-box packing: at least 2 in of cushioning on each side. 14. [FTC Green Guides, 16 CFR 260.12 Recyclable claims](https://www.law.cornell.edu/cfr/text/16/260.12) (regulator). Supports: unqualified recyclable claims need facilities for a substantial majority, at least 60 percent. 15. [Uline, 12 x 6 x 6 in Long Corrugated Boxes S-4128, product page](https://www.uline.com/Product/Detail/S-4128/Corrugated-Boxes-200-Test/12-x-12-x-12-Corrugated-Boxes) (spec sheet). Supports: box strength table: Fibre Box Handbook limits beside UPS guideline weights; 32 ECT 65 lb certificate, 30 lb UPS; 200# 65 lb and 40 lb; inside dimensions L x W x H, opens along the first dimension, C flute; dimensional weight 4 lb for a 12 x 6 x 6 in box. 16. [Uline, Multi-Depth Boxes](https://www.uline.com/BL_407/Multi-Depth-Boxes) (spec sheet). Supports: boxes creased at set heights to cut down and reduce dimensional weight. 17. [Uline, Kraft Easy-Fold Mailers](https://www.uline.com/BL_1301/Kraft-Easy-Fold-Mailers) (spec sheet). Supports: fold-over book mailers scored at variable depths, 200 lb test, B-flute. 18. [Uline, Moving Kits](https://www.uline.com/BL_7907/Moving-Kits) (spec sheet). Supports: moving boxes sold as small, medium, large, with double-wall dish and wardrobe boxes. 19. [EcoEnclose, padded envelope, poly, rigid and paper mailer ranges](https://www.ecoenclose.com/shop/padded-envelopes/) (spec sheet). Supports: padding types: bubble film, embossed paper bubbles, newspaper fill, expanded adhesive; poly and bubble mailers with tear strip and second adhesive strip for reuse; rigid mailers for flat goods that must not bend; paper mailers for soft goods; newspaper-padded mailer described as ideal for fragile items. 20. [EcoEnclose, Designing for Recyclability](https://www.ecoenclose.com/resources/designing-for-recyclability) (primer). Supports: all-poly bubble mailer recyclable; paper outside with poly bubble inside is not; sorters reject paper mailers with hidden plastic padding; plastic film must be source separated, not put in the household bin. 21. [Wikipedia, Corrugated fiberboard and Corrugated box design](https://en.wikipedia.org/wiki/Corrugated_fiberboard) (primer). Supports: C flute most common; E and F used for printed mailer boxes; letters follow invention order; boxes specified by internal dimensions; RSC most common, coded 0201; box maker's certificate on the underside: test, size limit, gross weight limit; long storage in high humidity calls for extra strength. 22. [Wikipedia, Dimensional weight](https://en.wikipedia.org/wiki/Dimensional_weight) (primer). Supports: fee is the greater of dimensional and actual weight; UPS domestic: 139 for daily rates above 1 cubic foot, 166 for retail rates (2016 to 2017 citations). 23. [Wikipedia, Padded envelope](https://en.wikipedia.org/wiki/Padded_envelope) (primer). Supports: padding is usually thick paper, bubble wrap or foam; life-cycle study: kraft newsprint mailer had higher impact than plastic bubble mailer.