For a dense item, the void fill that holds is the kind that does not crush: corrugated inserts, partitions and blocking, or an engineered foam enclosure. UPS says peanuts and crumpled paper "crush and shift under heavy loads," and it lists air bags, bubble wrap and crumpled kraft paper as cushioning for lightweight items. The familiar 2 inch rule is a lightweight-item rule too. For heavy items, the carriers talk about dense cushioning, bracing and blocking, not more loose fill.

Why do air pillows and crumpled paper fail under a heavy item?

Loose fill fails under a heavy item because it was made to fill space around light contents, not to carry load. UPS says so on its shipping heavy items page: "Expanded polystyrene peanuts and crumpled paper won't protect your shipment effectively because both materials crush and shift under heavy loads."

In transit, a dense item presses on whatever sits under it. Crumpled paper flattens a little with every bump, each bump opens a gap, and once there is a gap the item moves into the box wall with its full weight behind it. Peanuts migrate away from the load and settle.

Air pillows fail differently. A pillow keeps its shape only while its film holds the air. Under a heavy item, the load rests on a few pillows at a time, and a corner or edge can puncture one. UPS's packaging tips list air bags (inflatable packaging) as a material for lightweight items and say they are not for items with sharp corners or edges. When a pillow goes flat, the item has somewhere to go.

These materials fill a void. They do not brace an item.

Does the 2 inch rule apply to heavy items?

No: the 2 inch rule, as UPS writes it, is guidance for lightweight items. UPS's packaging tips call for "no less than two inches" of loose fill around lightweight items, and at least two inches of tightly crumpled kraft paper between the contents and the outer box. That spacing keeps a light item off the walls. It does not stop a dense item from compressing the fill.

The other carriers have their own versions:

FedEx's general packaging guidelines say to wrap each product in at least 2 in of air-cellular or foam cushioning as the first step of its box-in-box method.
USPS, in DMM section 601, says loose-fill cushioning must overfill the box before it is closed.

For heavy items, a different instruction matters more. UPS says that for packages over 70 lb you should "Use only dense cushioning material," and it recommends "customized corrugated board or engineered foam enclosures" to reinforce the rigidity of the outer box. USPS requires mailers to "Brace and cushion heavy items to prevent damage to other mailpieces." Neither instruction is about inches of fill. Both are about stopping movement.

What void fill actually holds a dense item?

The materials that hold a dense item are the rigid ones that block and brace it, not the soft ones that surround it.

Material	What the carrier sources say	For a heavy, dense item
Crumpled paper	UPS: crushes and shifts under heavy loads; listed for lightweight items	Do not rely on it
Air pillows (air bags)	UPS: for lightweight items; not for sharp corners or edges	Do not rely on them
Polystyrene peanuts	UPS: crush and shift under heavy loads. FedEx: one parts-specific exception (below)	Do not rely on them
Bubble wrap	UPS: listed for lightweight items. FedEx: air-cellular wrap on the inner product in its box-in-box method	Surface protection, not bracing
Corrugated inserts, partitions, liners, cut forms	USPS: interior containers, cut forms, partitions, dunnage and liners as blocking and bracing for high-density items. UPS: customized corrugated board over 70 lb	Yes: blocks and braces
Engineered foam enclosure	UPS: recommended for packages over 70 lb	Yes, when it fits the item

Corrugated blocking works because it is rigid: a pad cut to the box's inside dimensions, or partitions on every side, hold the item in place instead of surrounding it.

Blocking only helps if the outer wall can take the load. If you are unsure your carton is up to the weight, read box strength for heavy items first, because good blocking will not save a wall that buckles.

Do the carriers agree on loose fill for heavy items?

Mostly, with one documented exception in a FedEx guide for auto parts. UPS says peanuts crush and shift under heavy loads. FedEx's automotive packing guide recommends loose-fill peanuts as dunnage around flexplates and flywheels packed in double- or triple-wall boxes.

Read each statement as its carrier wrote it. The FedEx one covers specific parts in heavy-wall boxes shipped with FedEx; it is not a general rule for heavy items, and it says nothing about what UPS expects. If you ship flexplates or flywheels with FedEx, follow FedEx's guide for those parts. For other heavy items, and anything going by UPS, plan on corrugated blocking or an engineered foam enclosure.

USPS takes a third angle. Its DMM section 601 says heavy items must be stabilized, and that high-density heavy items should not be packed with fragile items unless they are carefully kept apart. The worry is a dense item damaging what sits near it, in your box and in the mail stream.

The carrier wording quoted here was checked on October 21, 2026. Packaging pages change, so reread your carrier's page before you standardize a pack.

How do you build a box-in-box for a heavy item?

A box-in-box puts the braced item in a snug inner box, then centers that inner box in an outer box with 3 in of cushioning on every side. UPS calls it the two-box method: an outer box 6 inches larger than the inner box in depth, width and length, with 3 inches of cushioning around the inner box. FedEx uses the same numbers: an outer box at least 6 in longer, wider and deeper, and 3 in of cushioning between the boxes on every side.

Example: the box math for a dense item that, with its blocking, fits a 14 x 12 x 10 in inner box (hypothetical dimensions).

Step (example)	Measurement
Inner box: item plus blocking	14 x 12 x 10 in
Add 6 in to each dimension	20 x 18 x 16 in outer box
Cushioning gap on each side	3 in
Inner box volume	1,680 cubic in
Outer box volume	5,760 cubic in

For a heavy item, fill that 3 in gap with material that will not settle: corrugated pads and partitions cut to fit each side, or the dense cushioning UPS calls for over 70 lb.

The outer box here has more than three times the volume of the inner one, and carriers can bill a large box by its size instead of its scale weight. Run the outer dimensions through the dimensional weight math before choosing a box-in-box over a single strong box with fitted blocking. Void fill is one decision among several in our guide to shipping heavy packages, and the full packing sequence is in how to pack a heavy box.

How do you check a heavy pack before you buy the label?

Try to make the item move: if anything shifts when you tilt or lift the closed box, the void fill is not holding.

Weigh the item. If the packed box will be over 70 lb, UPS calls for dense cushioning only, so drop loose fill from the plan.
Block the item first with corrugated pads, partitions, liners or an inner box, so it cannot slide. That is the bracing USPS asks for.
Center it "away from the sides, corners, top, and bottom," as FedEx puts it.
Wrap and tape all sharp edges and protrusions on odd-shaped items, per FedEx.
Keep dense and fragile items apart. USPS says they should not share a box unless carefully separated; a second box is often simpler.
Fill the last headspace with rigid material, so the closed flaps sit on something solid.
Close, tilt and lift. Tip the box onto each edge. A shift or a thud means a gap.
Measure the outer box and weigh the packed box. Those numbers, not the item's, belong on the label.

Where GoatLabels fits

GoatLabels does not pack the box; it prices the box you packed. Enter the outer box's measurements and the packed weight, and it rate-shops USPS, UPS and FedEx on every domestic parcel, and DHL on international lanes, from one account with one all-in price per rate, so you can compare a box-in-box against a single braced box before you buy. Labels are paid from a prepaid wallet, and carrier adjustments after delivery, such as re-weighs and dimension corrections, post to the same wallet. GoatLabels finds and drafts carrier refund claims for disputed re-weigh and dimensional weight surcharges.

The limits: a quote built on the inner box or the bare item can be adjusted later, so measure the outer box. GoatLabels does not book LTL or freight. Optional insurance is offered at checkout when the shipment lists an item and its value; claims for insured shipments that arrive damaged are filed from Settings > Insurance, and GoatLabels reviews them and pays approved amounts. Plan costs are on the pricing page.