Foams (table)

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A two-phase system consisting of bubbles in either a solid or liquid matrix. Examples of liquid foams include: froth, soap bubbles, shaving cream, whipped cream, meringue, and foamed hair products. Solid foam examples include: bread, Cork, Sponge, Coral, Wood, pumice stone, marshmallows, foam rubber, Styrofoam®, and many other synthetic polymers. Foams can be generated by mechanical (mixing, agitation) or chemical (gas producing reactions) methods.

Foams have been developed using various precursors, such as polymers, metals, ceramics and even plants, in order to produce low-density, lighter weight structures with increased mechanical properties. In general, the properties of a foam correlate to the shape and structure of their pores. The two main groups of structures are closed or open cells.

  • Closed-cell foams have a cellular structure with air bubbles trapped within individual pockets that produces rigid, insulating buoyant materials with high compressive strength.
  • Open-cell foams have an interconnected cellular structure in which air can flow through continuous channels; these foams are generally flexible and permeable.
FOAMS Production/
Characteristics Common Applications Commercial examples Working properties Risks
Chloroprene thermoset; closed-cell or open-cell Soft, flexible, form-fitting sponge rubber, with good thermal and moisture insulation; resistant to sunlight and oxidation; closed-cell is waterproof, open-cell is breathable; both are inert and flame resistant wetsuits; sports equipment, insulated food holders, mouse pads, vibration mats; gaskets, seals Neoprene May cause allergic reactions; attacked by most acids and organic solvents
Ethylene vinyl acetate (EVA or PEVA) thermoplastic, closed-cell Has wide density range; provides good insulation, chemical and moisture resistance; buoyant, durable; resistant to UV deterioration packaging; shoes, underlayment, marine and sports products, construction, toys, mats; shock absorber Evasote, Sponge Aero Rubber Easy to work with; can be heat formed Can emit vinegar odor; EVA (#7) can not be easily recycled.
Nylon (polyamide) thermoplastic, closed-cell Lightweight, tough, strong, very durable; resistant to high temperatures, weathering and most chemicals; does not absorb gases or water; thermal and acoustical insulator seals and gaskets, hard body armor padding, transmission seals, energy absorbing panels Nomex; Zotek-NB50; Polyamide-NB Can be heat formed and used in direct contact with objects Very inert
Polyethylene (PEF) thermoplastic, closed-cell Strong, resilient; shock-absorbing, good insulator, buoyant; water-resistant; inert to biological attack; can be recycled (#4) cushioning, packaging, flotation devices; not as good for cushioning as PUR in crates, but can work around that by using things like springs for shock absorption Ethafoam, Plastazote, Polyplank, Volara, Minicel, Cellaire; Sentinel; Supazote Many variations in thicknesses and texture, stiffer than polyurethane; can be heat-sealed Highly inert but best not to use in direct contact with objects; may emit methane and ethylene
Polypropylene (EPP) thermoplastic, closed-cell Lightweight, flexible, durable, non-dusting structural foam with very good cushioning properties; may have a longer lifetime than PE foams; readily resumes original shape; breathable; chemically inert; may be recycled (#5) shipping plants; lining boxes, flotation devices Microfoam; Propafoam; Polypro; Polyzote; Strandfoam May be used adjacent to objects Poor resistance to UV and high temperatures; not recommended for outdoor use
Polystyrene (expanded-EPS or extruded-XPS) thermoset, closed-cell XPS is extruded polystyrene is lightweight, rigid, dimensionally stable, resistant to moisture and heat; will not rot or mildew (non-biodegradable); XPS does not crush as easily EPS; used as a substitute for cardboard cups, food containers, egg cartons; craft projects, insulation Styrene foam; Styrofoam (EPS); Foamular; Fome-cor; Gatorfoam; Gatorplast; Ultraboard; Foamular; Blue Board (XPS) Stiff enough to hold plywood; can be built into a structure that has wood elements; easy to cut XPS may crumble releasing puffed beads at cut edges; degraded by sunlight; added flame retardants may release hazardous components; polystyrenes (#6) can be separated and downcycled into new products.
Polyurethane thermoset; open-cell Flexible, soft, good compression memory with uniform texture, wide variety of densities; good only for temporary uses (i.e. crates) or outer crates; Crates should be opened when possible to not let volatiles accumulate inside the crate Cushioning in furniture, packaging; sound insulation; vibration dampening; most desirable properties are its sponginess and ability to be compressed; museum transport (decreasing use); better for cushioning than polyethylenes; widely used for crates, outer crates, carts and A frames Tempur-pedic; Memory foam; Sorbothane; Corafoam; Coralight Must be lined with something like Nomex; good for small cavities because it is so pliable it gives the cavity a spongy quality; possible to re-use if not degraded not inert; deterioration (brittle, crumbly, discolored, acidic) with time that is accelerated by UV and humidity; hygroscopic; highly flammable (added flame retardants may release hazardous components); polyurethane can be separated and downcycled.
Polyvinyl chloride thermoset, closed-cell Flexible, durable, high density, resistant to water, and abrasions; used in many laminated foamboards gaskets; weatherstripping; flooring, outdoor and marine applications; signs and displays, scale models PVC Foam; Komapor; Komacel; Komatex; Forex; Sintra; Formalux Easily cut; can be heat formed Does not fully spring back after compression; produces noxious gases when hot; can not be recycled (#3) and it is hazardous to environment.
Silicone closed-cell Low density solid that provides excellent thermal insulation, resilience and flexibility; performs well over wide temperature range; resistant to ozone and UV; springs back fully even after long compressions cushions, seals, insulation Spaceloft insulation; Grey Silicone PSG; Bisco BF Have poor tear strength; silicones can be separated and downcycled; they are not biodegradable
Biobased foams plant materials (bamboo, straw, sugarcane); kraft pulp, methyl cellulose Water-soluble; biodegradable, compostable, recyclable; great thermal insulation; high shock absorption; resistant to UV degradation; difficult to make smooth; sometimes filled with clay as a plasticizer packaging food; packing peanuts Biofoam; GreenCell foam; Foam-MC Often laminated or sealed in synthetic plastic but this eliminates its recycling/biodegrading potential Moisture sensitive; susceptible to biological attack; can shrink, sag and crumble with age
Latex foams Sap from Hevea Brasiliensis trees Eco-friendly; hypoallergenic; long term shape retention; poor heat transfer; heavy; high shock absorption; expensive mattresses, pillows, cushions Foam rubber Degrades in UV; crumbles and yellows with age
Metal foam, see Aluminum foam closed-cell or open-cell Eco-friendly; nonflammable; long term shape retention; heavier than polymers; very strong but 5-25% weight of solid material; excellent impact absorption construction; sound insulation; architectural decoration Duocel Carbide- or diamond-tipped blades are required for machining
Ceramic foam generally open-cell Stiff, lightweight material that is tough and strong compared to a bulk ceramic thermal and acoustic insulation; pollutant filtration; structures and decoration Carbide- or diamond-tipped blades are required for machining

Synonyms and Related Terms

foams; expanded plastic; froth, suds

Collection Risks

Foams vary widely in their potential for off-gassing hazardous materials and should be tested prior to use.

Resources and Citations

  • Wikipedia: Foam Accessed Dec 2023
  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • Hoechst Celanese Corporation, Dictionary of Fiber & Textile Technology (older version called Man-made Fiber and Textile Dictionary, 1965), Hoechst Celanese Corporation, Charlotte NC, 1990
  • Random House, Webster's Encyclopedic Unabridged Dictionary of the English Language, Grammercy Book, New York, 1997
  • The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998
  • Art and Architecture Thesaurus Online,, J. Paul Getty Trust, Los Angeles, 2000