THERMAX™ Sheathing

A glass-fiber reinforced polyisocyanurate foam insulation laminated between 1 mil smooth, reflective aluminum foil facers on both sides that is especially appropriate for hourly rated assemblies.

Used In

  • Insulate residential and commercial walls
  • Residential closed (non-vented) crawl spaces
  • Interior basement walls
  • Interior walls of metal buildings

Product Advantages

  • Can be installed exposed to the interior without a thermal barrier
  • Reinforcing facers, along with chemical modifications, contribute to fire resistance and dimensional stability
  • Suited for hourly rated assemblies

Typical Physical Properties

These properties are typical but do not constitute specifications.

THERMAX™ Sheathing - U.S. Residential

Nominal Board Thickness(1), in R-Value(2)(3) Board Size, ft Edge Treatment
.50 3.3 4 x 8, 4 x 9, 4 x 10 Square Edge
.75 5.0 4 x 8, 4 x 9, 4 x 10 Square Edge
1.0 6.5 4 x 8, 4 x 9, 4 x 10 Square Edge
1.5 9.8 4 x 8, 4 x 9, 4 x 10 Square Edge, Shiplap
2.0 13.0 4 x 8, 4 x 9, 4 x 10 Square Edge, Shiplap

(1) Not all product sizes are available in all regions.

(2) R means resistance to heat flow. The higher the R-value, the greater the insulating power. R-values are expressed in ft2• h•°F/Btu. R-value determined by ASTM C518.

(3) Consult your Dow Seller or Technical Service Group for information on different R-values.

(4) Vertical compressive strength is measured at 10% deformation or at yield, whichever occurs first.

THERMAX™ Sheathing - U.S. Commercial

Nominal Board Thickness(1), in R-Value(2) Board Size, ft Edge Treatment Min Compressive Strength(3), psi
0.5 3.3 4' x 8' / 4' x 10' Square Edge 25
.75 4.9 4' x 8' / 4' x 10' Square Edge 25
1.0 6.5 4' x 8' / 4' x 10' Square Edge 25
1.25 8.1 4' x 8' / 4' x 10' Square Edge 25
1.50 9.8 4' x 8' / 4' x 10' Square Edge, Shiplap 25
1.55 10.1 4' x 8' / 4' x 10' Square Edge, Shiplap 25
2.0 13.0 4' x 8' / 4' x 10' Square Edge, Shiplap 25

(1) Not all product sizes are available in all regions.

(2) R means resistance to heat flow. The higher the R-value, the greater the insulating power. R-values are expressed in ft2• h•°F/Btu. R-value determined by ASTM C518.

(3) Vertical compressive strength is measured at 10% deformation or yield, whichever occurs first. Since Dow polyisocyanurate insulation is a visco-elastic material, adequate design safety factors should be used to prevent long-term creep. For static loads, 3:1 is suggested. For dynamic loads, 5:1 is suggested.

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