Packaging Reference Library · Technical Reference

Polyethylene and Polyurethane Foam

Polyethylene (PE) foam is firm, closed cell and resilient, while polyurethane (PU) foam is soft and open cell. Both are sold by density, and density plus thickness decide how well a foam cushions a given load.

Ref PK-0120ASTM D3575

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

Polyethylene foam is a closed-cell foam that resists water and chemicals and recovers well from repeated impacts. It comes as thin rolls, sheets and thick planks. Cross-linked PE has a finer cell and smoother surface.
Polyurethane foam is an open-cell foam that is soft and conforms to delicate shapes. Polyether PU is the common packaging grade. Polyester PU is firmer and is often used in cut-outs and case inserts. Convoluted ("egg crate") PU cushions irregular items.

How to identify

PE foam feels smooth and slightly waxy and springs back when pressed. It does not soak up water. PU foam feels like a sponge and absorbs water. Labels and spec sheets give density in pounds per cubic foot (pcf) or kilograms per cubic meter, color, thickness and whether the foam is anti-static.

PE vs PU foam

Feature	Polyethylene foam	Polyurethane foam
Cell structure	Closed cell	Open cell
Feel	Firm, resilient	Soft, spongy
Water absorption	Very low	High
Repeated impacts	Good	Fair
Typical forms	Rolls, sheets, planks, die-cut and routed inserts	Sheets, convoluted pads, case inserts
Fabrication	Saw, die cut, router, heat lamination	Die cut, convoluting, adhesive lamination
Typical uses	Heavy or fragile items, end caps, reusable trays	Light, delicate items, instrument cases

Density and cushioning

Density is the weight of a cubic foot of foam. Higher density foam is firmer and supports more load per square inch. Lower density foam is softer and protects light items better. Pick density and thickness from the foam maker's cushion curves using the product weight, the bearing area and the expected drop height.

Key points

PE foam is tested and classified under ASTM D3575. Spec sheets list compressive strength, tensile strength and other properties by that method.
Pink and black anti-static foams are made for electronics. Check whether the foam is anti-static or static dissipative for the job.
Laminated PE planks build thick inserts from thinner sheets.
PU foam can take a permanent set under a constant load. Avoid it for heavy items in long storage.

Common mistakes

Using soft PU foam under a heavy item that crushes it.
Picking the stiffest foam for a light item, which then sees more shock.
Assuming all pink foam is ESD safe.
Leaving foam inserts loose in an oversize box.

Governing standards: ASTM D3575 (flexible cellular materials made from olefin polymers); ASTM D3574 (flexible polyurethane foam test methods); ASTM D1596 (cushion testing).

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

More in Technical Reference

← All Packaging sheets