Foamed solids, generic
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Description
A two-phase system consisting of air pockets or bubbles in a solid matrix. 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. Solid foam examples include: bread, Cork, Sponge, Coral, Wood, pumice stone, marshmallows, foam rubber, Styrofoam®, and many other synthetic polymers. Additionally some are soft and spongy (foam rubber, polyethylene, etc.) or rigid and strong (polystyrene, epoxy). Steam, air, or an inert gas is mechanically added or chemically produced in the plastic resins during manufacture to form a cured open cellular structure. Closed-cell foams have individual non-connected bubbles while open-cell foams have an interconnected tunnels formed when the incorporated gas or steam escapes during cure.
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.
Synonyms and Related Terms
foamed plastic; goma espuma (Esp.); plastique expensé (Fr.); mousse de plastique (Fr.); plastic foam (AAT preferred); foam rubber; expanded plastic; cellular plastic; Styrofoam;
Comparison Table
| 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; 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 |
Risks
- Most foamed plastics are combustible.
- Many have the potential for off-gassing hazardous materials and should be tested prior to use.
Resources and Citations
- Wikipedia: Foam Accessed Dec 2023
- Theodore J. Reinhart, 'Glossary of Terms', Engineered Plastics, ASM International, 1988
- Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
- Pam Hatchfield, Pollutants in the Museum Environment, Archetype Press, London, 2002
- Van Nostrand's Scientific Encyclopedia, Douglas M. Considine (ed.), Van Nostrand Reinhold, New York, 1976
- Art and Architecture Thesaurus Online, https://www.getty.edu/research/tools/vocabulary/aat/, J. Paul Getty Trust, Los Angeles, 2000 Comment: plastic foam (preferred)