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Rigid & Flexible Foam Casting

Casting polyurethane foams

Polyurethane foams are chemically similar to their resin and rubber counterparts, however, foam casting is very different from rubber or resin casting. Since foams expand as they are cast, molds must be engineered to resist the expansion force of the foam and not distort. Most of our foams are "closed cell," or self-skinning formulas. Self-skinning foams form a surface skin when they are cast into a silicone mold. The more back pressure that is created in the casting process, the thicker, and more uniform the skin will become. Here are some important rules for foam casting:

  • Foam is sensitive to cold temperatures. Keep materials, molds, and the work area warm for best results.
  • Pigment foam only with PolyColor Pigments, 6800 Pigments, or other suitable, tested pigment. Adding acrylics or food coloring will cause problems with the foam chemistry.
  • Do not over load foam into closed molds or distortion will occur.
  • Mix accurately for best results.
  • Flexible and rigid foams work best in silicone molds.

Foams are measured by their expansion per cubic foot. A 2# foam for example, is 2 pounds per cubic foot once expanded and cured. This means that 1 pound of A mixed with 1 pound of B will yield a cubic foot of foam in free rise. If restricted, or cast in a closed mold, the expansion will be lower. The higher a foam"s number (or pounds per cubic foot), the denser the foam. Low density foams are typically 2 or 3 pound density. A high density foam would be 8-10 pounds. In this video we cover the basics of foam casting.

Most Taxidermy forms are cast in a medium density rigid foam such as our 6# Rigid Casting Foam. Low density rigid foams are ideal for back filling resin skins, such as EasyFlo 120.

Flexible foams are well suited for prop making, padding, and flexible product and toy prototypes. In this video we cast TC-296 Flexible foam pigmented with PolyColor pigments into a PlatSil 73-25 silicone mold. This process is ideal for prop making. The TC-296 is a flame rated foam that may be used for theme park and haunted house interiors that must comply with fire code.

Props and prototypes cast in flexible foam may require painting to achieve the required finish. Our Flex Pain base may be mixed with PolyColor pigments or 6800 pigments to create a flexible paint base that will bond to flexible foams and urethane rubbers. In this video we cast two TC-284 foam head props from a TinSil 80-30 mold. For the first cast, the TC-284 foam was pigmented with 6800 Flesh pigment. The second cast used a skin of FP-15 (FP-15 is one of our "casting rubbers." Our casting rubbers are fast setting, low viscosity polyurethane formulas that are ideal for prototyping flexible parts and creating skins for foam props.)  "sloshed" into the mold folowed by the TC-284 foam. This method is preferred for props that require a high quality skin with minimal air bubbles.

In this tutorial we explain the basics of casting our 6lb Density Rigid Casting Foam. Here we cast 6lb Density Rigid Foam into a 5110 silicone mold.