Structural foam molding (plastic pallets)
Also called: structural foam, SFM, low-pressure foam molding
Structural foam molding is a low-pressure injection process in which a gas or blowing agent foams the plastic core while a solid skin forms against the mold. It makes thick, rigid, heavy-duty plastic pallets.
In depth: Rackable plastic pallet: runners, reinforcement and racking ratings
Structural foam is a variant of injection molding. Molten resin with a blowing agent or gas is injected at low pressure, so the part has a dense skin and a lighter cellular core. Thick walls become possible without the sink marks and stresses that solid thick walls would have.
Typical characteristics
| Feature | Structural foam | Conventional injection |
|---|---|---|
| Mold pressure | Low | High |
| Tooling | Often aluminum, less costly | Steel, very costly |
| Walls | Thick, rigid | Thinner |
| Typical pallets | Heavy-duty rackable, drum and export pallets | Most catalog nestable and rackable pallets |
| Weakness | Can chip or chunk under fork impact | Better impact resistance |
Heavy-duty structural-foam 48 × 40 pallets are sold with static ratings up to 30,000 lb (13,600 kg) in manufacturers' catalogs. Dynamic and racking ratings are far lower and depend on the model.
Why it matters
Structural foam is the usual process for rigid, heavy plastic pallets that must carry high loads or span racks. Tooling is cheaper than conventional injection molding, but a new tool is still a large investment, so custom structural-foam designs are rare at normal order volumes. Buyers usually pick a catalog model.
On a spec sheet
Process is often listed on plastic pallet data sheets. Specify the requirement (load, rack span and orientation, temperature) and let suppliers propose models, stating the test standard behind each rating.
Related
- GlossaryInjection molding (plastic pallets)Injection molding forces molten plastic into a closed steel mold under high pressure. It produces most catalog plastic pallets with tight dimensions and fast cycles, but a new pallet mold only pays off at very high volumes.
- GlossaryHDPE (high-density polyethylene)HDPE (high-density polyethylene) is the most common resin for plastic pallets. It stays tough at low temperatures, which suits freezers and cold chains, but it is less stiff than polypropylene, which matters for rack deflection.
- TypesRackable plastic pallet: runners, reinforcement and racking ratingsA rackable plastic pallet is designed to sit in open-beam racking with nothing underneath. It has runners (3, 5 or 6) or a perimeter or cruciform base, often with steel reinforcement. Racking ratings for 48 × 40 in models are typically about 1,500–4,400 lb, valid only at the tested span and orientation.
- GuidesPlastic pallet buying guide: styles, resins, ratings and costChoose a plastic pallet by how it is handled and stored: nestable for cheap one-way use, stackable for floor stacking, rackable for open-beam racking. Compare static, dynamic and racking ratings only when the test standard and support match. New US prices run about $40–200 (2026 estimates).
- TypesPlastic pallets: types, materials, load ratings and how to buy themA plastic pallet is a molded or fabricated pallet made from HDPE or polypropylene. Types range from light nestable pallets (about 14–30 lb) to reinforced rackable pallets (about 35–70 lb). They are washable, ISPM 15 exempt and long-lived, cost several times more than wood, and carry three separate load ratings.
More in Materials
- GlossaryBark (on pallet lumber)Bark is the outer layer of a tree trunk. ISPM 15 requires wood packaging to be made from debarked wood, allowing only small remnants: pieces under 3 cm wide of any length, or wider pieces with a surface area under 50 cm².
- GlossaryCant (pallet lumber)A cant is a log that has been sawn flat on two or four sides. In the pallet industry it usually means the low-grade center of a hardwood log, left after grade lumber is cut from the outside, which is resawn into pallet parts.
- GlossaryComposite block (pallet)A composite block is a pallet block made from wood chips, particles or fibers bonded with resin under heat and pressure. It does not split like solid wood and, as processed wood, is exempt from ISPM 15 on its own.
- GlossaryCorrugated fiberboard (pallets and slip sheets)Corrugated fiberboard is a board made of a fluted paper medium glued between flat paper liners. It is used for boxes, and in pallet work for corrugated paper pallets, slip sheets, tier sheets and pallet runners.
- GlossaryCut stock (pallet components)Cut stock is lumber already sawn to the finished thickness, width and length of pallet parts, such as 5/8 × 3-1/2 × 40 in deckboards, ready for nailing. It is also called pallet stock or shook.
- GlossaryDouglas-fir (pallet lumber)Douglas-fir is a dense, strong softwood from western North America, also grown in Europe. It is species class 11 (Douglas-fir–larch) in the Uniform Standard and PDS, and class 33 in the European species list.
Last reviewed 2026-09-24. 245 words.