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	Soft, flexible, form-fitting sponge rubber, with good thermal and moisture insulation. Resistant to sunlight and oxidation	sports gloves, insulated food holders, knee and elbow pads, joint filler	Neoprene
Ethylene vinyl acetate	thermoplastic, closed-cell	Frequently used as foam sheet with a wide density range; provides good insulation, moisture resistance and can be heat formed; buoyant	packaging; shoes, underlayment, marine and sports products, construction, toys, mats	Evasote, Sponge Aero Rubber	Good chemical resistance and outdoor durability
Nylon	thermoplastic, closed-cell	Resistant to high temperatures; can be thermoformed; low weight, buoyancy; thermal and acoustical insulator; very durable	seals and gaskets, hard body armor padding, transmission seals, energy absorbing panels	Nomex;		Very clean; can be used in direct contact with objects
Polyethylene	thermoplastic, closed-cell	strong, resilient; shock-absorbing, good insulator, buoyant; water-resistant; can be heat sealed	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	Variations in thicknesses and texture, but generally stiffer than polyurethane	Highly inert but best not to use in direct contact with objects.
Polypropylene	thermoplastic, closed-cell	Durable, non-dusting structural foam with very good cushioning properties; may have a longer lifetime than PE foams	shipping plants; lining boxes, flotation devices	Microfoam; Propafoam; Polypro; Zotefoam; Polyzote
Polystyrene	thermoset, closed-cell	XPS is extruded polystyrene. It is rigid, thermal insulation, lightweight, moisture resistant; will not rot or mildew (non-biodegradable). Crumbles and produces puffed beads. XPS does not crush as easily eps	cups, food containers, egg cartons	Styrene foam; Styrofoam; Foamular; Fome-cor; Gatorfoam; Gatorplast; Ultraboard	Stiff enough to hold plywood; can be built into a structure that has wood elements
Polyurethane	thermoset; open-cell	Flexible, soft, good compression memory with uniform texture, burns easily;	cushioning in furniture, packaging; sound insulation; vibration dampening; most desirable properties are its sponginess and ability ot be compressed; museum transport, perhaps not as widely used anymore; better for cushioning that the polyethylenes; widely used for crates, outer crates; used for carts, A frames	Polyurethane flexible foam wedges; Tempur-pedic	need to line it with something like Nomex; good for small cavities because it is so pliable it gives the cavity a spongy quality; possible to re-use it if its ok quality	not inert; deteriorates over time; must be lined with something; good for temporary uses (i.e. crates) or outer crates; Crates should be opened when possible to not let volatiles accumulate inside the crate, hygroscopic
Polyvinyl chloride	thermoset, closed-cell	Flexible, durable, high density, resistant to water, oil and chemicals; produces noxious gases when hot	gaskets; weatherstripping; flooring, outdoor and marine applications	PVC Foam; Komapor; Komacel; Komatex; Forex; Sintra; Formalux
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; crumbles easily; often encased in plastic bags	packaging food; packing peanuts	Biofoam; GreenCell foam; Foam-MC
Latex foams	Sap from Hevea Brasiliensis trees	Eco-friendly; hypoallergenic; long term shape retention; poor heat transfer; heavy; high shock absorption; degrades in UV; crumbles with age; expensive	mattresses, pillows, cushions
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