Dow Thermax Sheathing 4' x 8' Polyiso (All Sizes) Polyiso Thermax Sheathing
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Dow Thermax Sheathing 4' x 8' Polyiso (All Sizes)


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Estimated Delivery Time 7-10 Working Days

THERMAX Sheathing is specially designed to have a Class A fire rating and can be used in a range of concealed and exposed applications, above and below grade. Because of the improved fire performance it is best suited for hourly rated assemblies. It has nominal 1.0 mil, smooth aluminum foil facers on both sides. THERMAX Sheathing effectively reduces condensation for exceptional moisture protection.

Thickness R-Value Sq Ft/Bag
0.5" R3 32
1" R6 32
1.5" R10 32
2" R13 32

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


Other Related Products

If you're looking for other options for sheathing, here are some products that might meet your needs:

Rmax Ultra-Max HD High Density Coverboard 4' x 8' x 0.5": This product is a high-density cover board designed to be used with low-slope roofs. It can also be used as a thermal barrier or coverboard over a variety of substrates.

Kooltherm K9 Internal Insulation Board (All Thicknesses): This insulation board is made from rigid thermoset phenolic insulation core with aluminum foil facings on both sides. It is designed for use in internal walls, floors, and roofs.

Kingspan Kooltherm K12 Internal Insulation Board (All Thicknesses): This is another internal insulation board option made by Kingspan. It has a fiber-free rigid thermoset phenolic insulation core with low emissivity foil facings on both sides.

Kingspan GreenGuard LG Type VI 40 PSI XPS Insulation Board 2' x 4' x 8': This product is a high-performance insulation board that has a closed-cell structure and a high compressive strength. It is made from extruded polystyrene (XPS) and is designed for use in applications such as foundation walls and roofs.

Kingspan GreenGuard LG Type VII 60 PSI XPS Insulation Board 2' x 2' x 8' and Kingspan GreenGuard LG Type VII 60 PSI XPS Insulation Board 2' x 4' x 8' (48 Boards): These are high-performance insulation boards made from extruded polystyrene (XPS) that are designed for use in demanding applications such as foundation walls and roofing systems. They have a closed-cell structure and a high compressive strength.

Owens Corning Foamular NGX 250 4' x 8' x 1" Insulation Board: This is a rigid foam insulation board made from a sustainable material. It has a high R-value and can be used in a variety of applications, including walls, roofs, and below-grade foundations.

Rmax Durasheath-3 Insulation Board 4' x 8': This is a rigid foam insulation board designed for use in walls and roofs


Frequently Asked Questions

What is Dow Thermax Sheathing 4' x 8' Polyiso? Dow Thermax Sheathing is a polyisocyanurate insulation panel designed for use in walls, roofs, and foundations. It provides high thermal efficiency and water resistance, making it an excellent choice for a variety of applications.

What are the dimensions of the panels? The panels are 4 feet by 8 feet in size, with a thickness of either 1 inch, 1.5 inches, 2 inches, or 3 inches, depending on the specific product.

How is Dow Thermax Sheathing installed? The panels are typically installed over the structural framing of a building using mechanical fasteners, and then covered with a compatible air barrier system. Specific installation instructions may vary depending on the application.

Is Dow Thermax Sheathing environmentally friendly? Dow Thermax Sheathing is manufactured with a blowing agent that has zero ozone depletion potential and low global warming potential, making it an environmentally responsible choice for insulation.

Can Dow Thermax Sheathing be used in below-grade applications? Yes, Dow Thermax Sheathing is suitable for use in below-grade applications, such as foundations, where it can help prevent moisture infiltration and improve energy efficiency.

How does Dow Thermax Sheathing compare to other insulation materials? Dow Thermax Sheathing offers superior thermal efficiency and moisture resistance compared to many other types of insulation materials, making it a popular choice for commercial and residential applications.

Is Dow Thermax Sheathing fire-resistant? Dow Thermax Sheathing has a Class A fire rating, which is the highest rating for building materials. It has been tested to meet fire safety standards and can help improve the fire resistance of a building.

How long does Dow Thermax Sheathing last? Dow Thermax Sheathing is designed to last for the lifetime of the building in which it is installed. Its high-quality materials and construction ensure long-term performance and energy efficiency.


Customer Feedback

The Dow Thermax Sheathing 4' x 8' Polyiso is an excellent insulation board for commercial and residential construction projects. As one of the highest performing rigid insulation products on the market, it provides exceptional thermal resistance with an R-value of 6.0 per inch of thickness.

One of the great advantages of this product is its versatility. The Dow Thermax Sheathing can be used on walls, roofs, and foundations, making it a great all-around solution for any construction project. It is also resistant to moisture, ensuring long-lasting performance and preventing mold growth.

Another feature that stands out is its lightweight nature, which makes it easy to handle and install. The product is also easy to cut to size, which can save a considerable amount of time and effort on the job site.

Overall, the Dow Thermax Sheathing 4' x 8' Polyiso is an excellent choice for those looking for a high-performance insulation solution that is easy to work with and can be used in a wide range of applications. The product has received high praise from many customers, who have noted its durability and effectiveness. I would highly recommend this product to anyone looking for a reliable and versatile insulation solution.

Product Length 96"
Product Width 48"
R-Value R13
Brand Dow
Material Facing Foil-Faced
Material Type Polyiso
Product Type Batt,Rigid Board

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Delivery will always take place on a weekday (Mon - Fri).
For information on delivery costs and more view our delivery info page.