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, providing structural support while allowing for lightweight construction. Whether the core of the board is made of gypsum or other materials, facers help ensure the board performs reliably during and after installation while protecting against the elements. 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 performs. 

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, we offer both coated and uncoated facer solutions, with coated nonwovens produced in Europe and uncoated facers manufactured in North America using adjusted fiber blends. These approaches 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 - and enhance barrier properties. Both options are available globally, giving customers flexibility to choose the best solution for their specific product requirements. 

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 enhanced foldability resulting in crisp edges 

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 permeability, water absorption, flexural strength, and thermal resistance - these are just some of the benchmarks we have the ability to customize for our customers. 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. Global 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 ensure global supply and regional support. Combined with our comprehensive portfolio, reliability, and deep technical expertise, 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.