Why Exterior Sheathing Needs a Tough Partner – And Why Our Fiberglass Nonwovens Are Up for the Job

In the world of building construction, not every component gets the spotlight - but some play a crucial behind-the-scenes role. One example? The facers used in exterior sheathing boards. Facers are technical layers, typically made from fiberglass nonwovens, that can be applied to both the front and back sides of sheathing panels. These panels often form the outer shell of a building’s wall structure, providing stability and protection before the final exterior finish is added. Whether the core of the board is made of gypsum, OSB or other materials, facers help ensure the board performs reliably during and after installation. At Johns Manville Engineered Products, we manufacture high-quality fiberglass nonwovens used as facers for a wide variety of sheathing applications. These materials may not be visible in the final building,  but they’re essential to how the board behaves. 

Why Facers Matter in Sheathing Systems 

The job of a facer is demanding. It needs to: 

• Support the mechanical integrity of the board 
• Ensure strong adhesion to the core material 
• Prevent gypsum slurry from bleeding through during gypsum board production  
• Allow for efficient water vapor transmission rate 
• Withstand tough environmental conditions like UV exposure, moisture, and airborne chemicals 
• Contribute to fire performance and other safety-related properties 

To balance these needs, our nonwovens can be treated with surface adjusting coatings depending on performance requirements. These coatings are key to managing air permeability: low enough to contain the core material, but open enough to support proper drying during the production process of board manufacturers. 

Color options are also available and can be tailored to customer needs, especially when the board will be visible on-site during construction. In some cases, customers may choose to print logos or branding on the facer surface as part of their process. 

From Production Line to Jobsite: Performance at Every Step 

A high-performing facer must support the board’s function in the field but also run smoothly during manufacturing. For example, the material must be: 

• Compatible with other raw materials used in board production 
• Low in fiber and dust formation to protect machine operators and avoid machine contamination 
• Mechanically strong without being brittle to avoid cracks during handling and cutting 
• Easy to groove for foldable boards 

Our fiberglass nonwovens are engineered to meet these demands while maintaining consistent quality and reliable supply. 

Put to the Test: What Sheathing Boards Need to Prove 

We know that exterior sheathing boards need to pass a wide range of demanding tests before they ever make it to a jobsite and we design our fiberglass nonwoven facers with that reality in mind. Whether it’s mold resistance in high-humidity conditions, weathering simulations that replicate years of sun and rain, or fire performance testing under intense heat, these requirements are critical to product approval and market success. Water vapor permeance, water absorption, flexural strength, thermal resistance, and vertical deflection - these are just some of the benchmarks that our customers need to hit. And every one of them places specific demands on the facer materials.  

At Johns Manville, we understand these challenges and what’s at stake. That’s why we work closely with our partners to support them not just with high-quality glass mats, but also with the technical expertise and service they need to navigate testing, compliance, and production efficiently. From early product development to production trials and fine-tuning, we’re here to help.  

Trusted Experience. Local Supply. Reliable Partnership. 

With decades of experience, we are a partner that understands your challenges and speaks your technical language. Our manufacturing sites in both Europe and North America mean better supply security, shorter lead times, and faster support when you need it most. Our glass mats for exterior sheathing are engineered with precision and supported by a customer-focused team that’s ready to help. 

Let’s build smarter - together.