Foams (table)

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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; Viton; Zotek 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