Fleece: From wool sweater to roof membrane

To most people, fleece is a cozy synthetic or wool textile, brushed on one side to trap warmth and worn as a mid-layer jacket or pullover. It feels substantial, stretchy, and comfortable against skin. In construction, fleece is something altogether thinner and more specialized: a nonwoven mat or membrane backer composed of matted fibers, typically polyester or polypropylene, that serves as a support layer or weatherproofing component.

In roofing and waterproofing, fleece is engineered to sit between structural surfaces and finished membranes. It acts as a separation and reinforcement layer, preventing the membrane from adhering directly to the substrate and reducing the risk of puncture or tearing. The fibers are compressed and bonded, not knitted or woven, creating a permeable but stable backing. Thicknesses range from 100 to 400 grams per square meter, far denser than apparel fleece yet still flexible enough to conform to irregular surfaces.

The term migrated from textile production, where fleece has meant a soft raised fabric for centuries. Textile producers adopted the name for the brushed material itself; construction professionals borrowed it for the nonwoven membranes that visually and tactilely resembled that same fuzzy character. The shared quality is the fiber matrix: loose, interlocked fibers that diffuse air and water while providing a cushioning effect.

In textile production, fleece remains the finished good, sewn into garments sold as fleeceware. In construction, it is an intermediate component, a backer or separator that rarely appears in the final structure but proves essential to durability. Both rely on fiber technology, but one prioritizes comfort and the other prioritizes longevity and barrier performance.