Foams (table)

Description

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/ Structure	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
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	May be used adjacent to objects	Poor resistance to UV and high temperatures; not recommended for outdoor use
Polystyrene	thermoset, closed-cell	XPS is extruded polystyrene is rigid, thermal insulation, lightweight, moisture resistant; will not rot or mildew (non-biodegradable); XPS does not crush as easily EPS	cups, food containers, egg cartons; craft projects, insulation	Styrene foam; Styrofoam; Foamular; Fome-cor; Gatorfoam; Gatorplast; Ultraboard	Stiff enough to hold plywood; can be built into a structure that has wood elements	XPS may crumble releasing puffed beads at cut edges; degraded by sunlight; added flame retardants may release hazardous components
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	Polyurethane flexible foam wedges; 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 its ok quality	not inert; deterioration (brittle, crumbly, discolored, acidic) with time and accelerated with UV and humidity; hygroscopic; highly flammable (added flame retardants may release hazardous components)
Polyvinyl chloride	thermoset, closed-cell	Flexible, durable, high density, resistant to water, oil and chemicals;	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	Produces noxious gases when hot
Silicone	closed-cell	Low density solid that provides excellent thermal insulation, resilience and flexibility; performs well at extreme temperatures; resistant to ozone and UV	cushions, seals, insulation	Spaceloft insulation; Grey Silicone PSG; Bisco BF
Biobased foams	plant materials; kraft pulp, methyl cellulose	Water-soluble; biodegradable, compostable, recyclable; great thermal insulation; high shock absorption; resistant to UV degradation; difficult to make smooth; often encased in plastic bags	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, http://www.getty.edu/research/tools/vocabulary/aat/, J. Paul Getty Trust, Los Angeles, 2000