FOAMULAR R-1 Fanfold XPS Underlayment, 1/4 in. x 4 ft. x 50 ft

High-performance XPS fanfold underlayment designed for re-siding and wall sheathing. Moisture-resistant and easy to cut, it delivers R-1 thermal performance in a flexible, square-edge format ideal for smooth, energy-efficient cladding prep.

Key Features:

Moisture Resistance: XPS construction retains R-value even in wet conditions
Easy Handling: Lightweight panels score, cut, and install without special tools
Flexible Fanfold Design: 50 ft. continuous coverage speeds re-siding prep
Square Edge Fit: Flush seams for smooth sheathing under new siding
Environmental Certifications: GREENGUARD Gold; listed in ENERGY STAR Seals and Insulates

Please check the Product Data Sheet Here

Specifications Table:

Specification	Details
Insulation Type	Foam Board Insulation (XPS)
Insulation R-Value	R-1
Compressive Strength	25 psi
Thickness	0.25 in (1/4 in.)
Width	48 in
Length	50 ft
Coverage Area	200 sq ft
Edge Profile	Square Edge
Faced or Unfaced	Unfaced
Interior/Exterior Use	Interior (re-siding sheathing)
Insulation Location	Re-Siding
Compatible Install Surface	Concrete, Plywood, Wood
Number of Pieces	1
Pack Size	1
Product Weight	13.2 lb
Sheathing Type	XPS
Warranty	Limited Lifetime
Certifications	GREENGUARD Gold; ENERGY STAR Seals and Insulates listing
Environmental Note	Manufactured with a blowing agent with >80% reduction in global warming potential vs. legacy FOAMULAR XPS

Frequently Asked Questions (FAQ):

Q: Can this be used under new siding?
A: Yes, its designed as a re-siding fanfold underlayment to create a smooth, insulated surface.

Q: Is it suitable for damp areas?
A: The XPS foam resists moisture and maintains its R-value after exposure to water.

Q: Do I need special tools to install it?
A: No. Panels are easy to score and cut with common utility knives and install with standard fasteners or foamboard adhesive.

Q: What are the dimensions and coverage?
A: Thickness 1/4 in., width 48 in., length 50 ft; covers approximately 200 sq. ft.

Q: Is it soundproof?
A: No, this product is not rated for STC and does not provide soundproofing.

Streamlined Sheathing for a Flawless Facade

FOAMULARs fanfold underlayment creates an impeccably smooth canvas beneath fresh siding, elevating curb appeal while quietly boosting energy performance. The flexible, square-edge design glides over exterior walls for clean lines and a refined finish. Pair it with crisp fiber-cement or modern vinyl profiles to achieve a tailored, contemporary look. Its a smart, luxurious layer that makes exteriors feel deliberate and beautifully composed.

Upgrade your re-siding project with FOAMULAR fanfold underlayment for smoother walls and lasting energy savingsadd to cart today.

Installation

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