Polyisocyanurate Boards

Thermax by DOW Chemical

Thermax Metal Building Board provides both insulation value and an interior finish system for interior walls in metal buildings. Thermax insulation board is fire rated for exposed applications in metal buildings and installs quickly in walls and ceilings – inside and outside of purlins, trusses or bar joints. Board insulation is also used in standing seam metal roof applications. Boards are lightweight and can be sawed or cut with a knife. In order to meet fire rating specifications, the surface of the insulation at all joints must be continuously sealed with tape or with a joint closure system. R-values can be found within each product information sheet below.

  • Foil faced or White faced
  • White embossed – Light Duty, Medium, Heavy Duty, and Heavy Duty Plus


  • Thermax Sheathing
  • Thermax Metal Building Board
  • Thermax Light Duty Insulation
  • Thermax Heavy Duty Insulation
  • Thermax Heavy Duty Plus Insulation
  • R-Value Comparison Information Sheet
  • Dow Commercial Products Selector Guide

Rmax A Less Expensive Alternative to Thermax

Rmax TSX-8500 Series, For Metal, Agricultural and Light Commercial Applications

Rmax TSX-8500 Series is a rigid, foam plastic, thermal insulation board composed of environmentally sound, closed cell, polyisocyanurate foam bonded to a glass fiber reinforced heavy 1.5 mil aluminum foil facer on the exposed side of the board. TSX-8500 Series is designed for use without a thermal barrier in metal buildings and other light commercial structures, as well as, for basement and interior walls, agricultural, post frame and cold storage applications where local building codes will allow. It has been tested per UL1715. A variety of thicknesses and lengths are available for ease of application. TSX 8500 applications and specifications are further described in ICC-ES report ESR-1864.

Rmax Thermasheath-3 and Thermasheath Plus-3, For Lamination of Metal and Other Facing Materials

Both Thermasheath-3 and Thermasheath Plus-3 feature environmentally sound, closed cell, polyiso foam cores bonded to foil facers. Thermasheath-3 has reinforced aluminum foil facers on each side. Thermasheath Plus-3 uses glass fiber reinforced foil facers on each side for added strength and durability. Both products make excellent substrates for laminating a variety of facing materials including metal panels, FRP panels, OSB or plywood, as well as, other materials. Both products are available in many thicknesses and lengths. For specific uses and other information about these and other Rmax specialty products consult your Rmax sales representative or regional sales office. Thermasheath-3 applications and specifications are further described in ICC-ES report ESR-1864

Other Products


This thermal insulation board is composed of a polyiso foam core bonded to a glass fiber reinforced 1.5 mil white aluminum foil facer on the exposed side of the board. This product is designed and tested for use without the use of a thermal barrier (UL1715) in pre-engineered metal buildings, laminate panel products and other similar applications.


Specialized applications, such as, tank insulation, wineries and certain cold storage applications where a foil faced product is specified. This product is a rigid foam plastic thermal insulation board composed of polyiso foam bonded to reinforced aluminum foil facers on each side.


This product has been used successfully by the log home, modular building and metal roofing manufacturers. It is a rigid closed cell foam insulation composed of a polyiso core bonded to glass fiber/organic mat facers on each side.

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