Why use polyurethane foam? | General Plastics
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Why Use Polyurethane Foam


Polyurethane (PU) foam is created when isocyanate and polyol are reacted. It becomes polyurethane foam when gas is introduced, either via reaction of the isocyanate with water, or with blowing agents.  General Plastics has a number of proprietary formulations which have been created for meeting a wide variety of thermal or physical property requirements.

Rigid PU foams are useful in composite constructions. Polyurethane foams are made in large blocks through either a continuous-reaction process or in a batch process. The blocks are then cut into sheets or other shapes. They may also be individually molded or cast into custom part shapes.

Integral-skin foams, or self-skinning foams, couple a high-density skin and a low-density core. Self-skinning foams are available in either flexible or rigid foam formulations.  The skin is beneficial due to the ability to mold custom textures for decoration or to impart abrasion or chemical resistant properties.


  • Closed cell rigid polyurethane foams are plastics created of bubbles that are continuous and completely spherical or oblong
  • Open cell flexible polyurethane foams are plastics with cell walls that are incomplete, and contain holes through which liquid and air can easily travel

Our Closed cell products are strong, durable, rigid, do not absorb water and are used for many different purposes. Their variety of applications lend themselves to industries such as such as marine, aerospace, construction, recreation, modeling and more. The other category of polyurethane foams, open celled, are used for load deflection applications, in industries such as aerospace, defense, automotive and others.

Please note that General Plastics does NOT produce or supply:

  • Soft cushion foam, sold in rolls
  • Polyurethane bags
  • Spray polyurethane foam / residential insulation


Foam densities range from approximately 2 to 60 lbs. per cubic foot (48 to 961 kg/m3). Unlike thermoplastic foams (PVC, SAN,), the unit cost of polyurethane foam increases in a linear fashion with density, so a 20-lbs.-per-cubic foot PU foam will be approximate twice the cost of a 10-lb. foam.

Foams of the same density can vary considerably in mechanical properties, depending on the foam production process. Different production methods may require unique chemical formulations and foam curing temperatures.  When beginning your foam selection process, it is important to reference the information on the Technical Data Sheet to ensure that the appropriate foam type is being used to meet your application’s property requirements.

If flammability is a concern, find out what kind of blowing agent is being used to create cells in the foam: Many producers use carbon dioxide (a byproduct of the foam-making chemical reaction) to create cells in their foams. Other producers have changed blowing agents in their low-density foam manufacturing processes. Switching from chlorofluorocarbon (HCFC, HFC) to pentane can negatively impact the foam’s flame resistance.


General Plastics’ premier closed-cell rigid and self-skinning molded polyurethane foams are used for high-performance applications by original equipment manufacturers, particularly in the aerospace, defense, marine, nuclear and other industries. Typically, they are used in tooling and mold making; as composite core; prototyping material; for protection of explosive or radioactive materials; and as a wood substitute for three-dimensional signs, displays and sculptures.


  • General Plastics is certified to ISO 9001:2015/AS9100D and meets NQA, MIL-1-45208A and MIL-P-26541 requirements.
  • Our aerospace-grade foams satisfy such specifications as Boeing Company D6-82479, BMS 8-133, BMS 8-436 and FAR 25.853 E-84,
  • If you require additional information regarding our certifications and qualifications, please call us.


  • Depend on our products for consistency – block to block, board to board, batch to batch.
  • All General Plastics products are manufactured in the United States in Tacoma, Washington.
  • Expect consistent density throughout sheets and buns – density gradient is less than +/- 10% of nominal density, and frequently closer to +/- 5%.
  • Precise bun trimming and horizontal band saw cutting creates cut sheets that are square and true.
  • Does not degrade, crack or change in chemical properties over time.


  • Depending on the density of the foam, our standard sheet sizes are 48” x 96” (122sm x 244cm) and 18” x 100” (46cm x 254cm).
  • We can supply buns up to 30″ inches (76cm) in height up to 60” (152cm) wide and up to 120″ (304cm) in length, depending on foam density – inquire about custom block size availability and cost.
  • We can provide machine tolerance from .005″ (0.0127cm) to 0.060″ (0.152cm).


  • Smooth, uniform, grain-free cell structure supports very fine surface finishes
  • Tough enough to support crisp cutting and excellent edge definition
  • Easily cut, carved and shaped, even with common woodworking tools
  • Foam is easily machined or CNC-milled without creating static
  • Most formulations contain no glass-bead or glass fiber fillers to compromise foam strength or damage cutting tools


  • Dimensionally stable – sheets do not warp, twist or bow
  • Can withstand extreme heat or cold
  • Offers good strength, rigidity and stability even at high heat
  • Does not absorb water, rot, decompose or dissolve in subgrade applications
  • Highly resistant to most chemicals and solvents even when heat-formed
  • Our products bond easily using a variety of bonding materials, including to metals and fiberglass laminating resins
  • Compatible with grouts, adhesives and concrete
  • Easy to finish with nearly any resin or coating system; minimal paint absorption


  • LAST-A-FOAM®products are CFC- and VOC-free.
  • They do not emit toxic fumes or leach chemicals into surrounding soil.
  • The material is biologically and chemically inert, so it does not support fungus or attract rodents and insects.
  • Many of our foam products are flame-retardant and self-extinguishing.


General Plastics manufactures commercial high-density foam products that are eco-friendly. Our “green” content combines post-industrial, post-consumer and rapidly renewable material resources.

Find green content in General Plastics’ LAST-A-FOAM® FR-4500, FR-4600 (Sign Foam 4), FR-7100 and R-9300 foams series. The percentage of green content varies by product line and density.

For example:

  • Each sheet of our FR-4500 product in the 6 lb. density diverts the equivalent of 32 water bottles from landfills
  • In the 50 lb. density, each sheet of our FR-4500 foam diverts the equivalent of 512 water bottles from landfills.
  • Our R-9300 Continuous Insulation Series foam blocks for industrial and cold-storage building construction applications may contribute to LEED certification with material containing up to 11% green content.


For full details on these aspects of working with our HDU (high-density urethane) materials, please refer to our User Guide to Tooling and Molds.

The Tooling & Molds User Guide covers the following topics:

  • Bonding and Adhesives
  • Cutting and Tooling
  • Colors, Coating Painting

Colors, Coating and Painting

Our flexible foams are white, and most of our rigid foams are yellow. Depending on the quantity, we can also formulate specific colors. Be aware that exposure to UV lighting will darken the exterior color of these foams. If appearance is a concern, we recommend painting them with an opaque coating.

Our polyurethane foams accept any paint finish and absorb very little paint.

Recommended coatings include automotive or woodworking grades. For outdoor use, acrylic-latex paint or enamel works well.

Thermal Properties

Refer to our technical data sheets (TDS) for thermal properties of our foams. Note that these numbers are approximate, and we recommend that you test the product for your particular application.

Our Product Naming System 

Most General Plastics polyurethane foam series products are identified by their foam category, density and often other essential characteristics as follows:

Rigid Foam Products, with the exception of our TR-Marine foams, start “FR” for Flame-retardant Rigid, or just the letter “R” for rigid, followed by the series number and foam density:


  • R-3315 – Rigid 3300 Submersible Foam Series, 15 lbs. per cubic ft. density
  • FR-3720 – Flame-retardant, Rigid 3700 Performance Core Series, 20 lbs. per cubic ft. density