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FR-3700 is a CFC-free, rigid, closed-cell, flame-retardant polyurethane foam available in densities ranging from 3 to 40 pounds per cubic foot. It exhibits a high strength-to-weight ratio due to its cellular structure and cross-linked resin. Because of its closed-cell structure, LAST-A-FOAM® FR-3700 has great resistance to water absorption, and will not swell, crack, or split on exposure to water. This series is non-abrasive and can be machined with standard high-speed steel (HSS) cutting tools. It can also be cut cleanly with water jets and traditional wood-carving tools. This flame-retardant polyurethane (PU) foam particularly supports the following industries.


FR-3700 meets the requirements of aircraft BMS 8-133. This rigid, polyurethane foam is comparable to the FR-6700 in strength, temperature resistance and flammability performance. However, the FR-3700 is tougher (less friable) for cutting crisper edges.


High-density rigid polyurethane FR-3700 foam is used to simulate human bone as a test medium within the medical device industry.



FR-3700 foams are chosen for nuclear material applications and transportation of extremely hazardous waste. When used as an impact- and fire-insulation liner in transport containers, FR-3700 can be engineered to provide the ultimate in fire and collision protection for hazardous cargo, outperforming wood and other polymeric materials. The FR-3700 formulation is specially designed to allow predictable impact-absorption performance under dynamic loading. At the same time, it provides an intumescent char layer that insulates and protects hazardous materials, even when exposed to pool-fire conditions.

In particular, our FR-3700 foam has a solid history of successful use in radioactive materials (RAM) transportation packages. The regulations governing RAM packages often require energy absorption of 30-foot free drops and exposure to a 1,475°F, 30-minute fire under accident conditions. Our FR-3700 series foam is one of the very few materials that can support the RAM package design in mitigating both mechanical and thermal energy.

View a demonstration of how the FR-3700 Performance Core Series protects nuclear cargo from an impact on our YouTube page or download our research paper on polyurethane foam as an impact mitigation and flame retardant material.


Use LAST-A-FOAM® 3700 Performance Core Series for constructing durable, weatherproof radomes. Impervious to moisture and transparent to radio signals, they protect marine, aerospace and recreational microwave antennas. Their high Tg suits prepregs that cure at higher temperatures. Or, let our Production Services team fabricate completed radomes using fiberglass prepregs from your specs.


FR-3700 tooling board machines well and is well suited for machining complex shapes for detailed part profiles. It is recommended that you do a rough cut first, leaving 1-3 mm of material for finishing. Use caution at edges and tight corners to avoid chipping at the start of a new pathway and when exiting the foam. See our Tooling & Molds User Guide for more information like roughing speed, finishing speed, and other machining information.



  • Stable and inert
  • Flame retardant
  • High strength-to-weight ratio from cross-linked resin
  • Resistant to most chemicals and solvents
  • Easily shaped with common woodworking tools
  • Performs well as wood replacement
  • Will not support fungal growth
  • Max use temperature of 260°F (127°C)


  • Models and design prototypes
  • Composite core, especially where flame retardation is important
  • Honeycomb edge closeout for aircraft interior sandwich panels used in overhead storage bins, passenger cabin class dividers, galleys and lavatories
  • Radioactive materials (RAM) transportation packages
  • Impact- and fire-insulation liner for hazardous waste containers
  • Vacuum form dies and mold patterns
  • Artificial human bone test media
  • Core material for composite prostheses
  • Load bearing
  • Dielectric material for radomes and antennas

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