What is ice and water shield made of?
Short answer. Most ice and water shield is a sheet of rubberized asphalt, meaning asphalt modified with polymers such as SBS that make it sticky, flexible and self-sealing, bonded to a top surface of plastic film, woven fabric or mineral granules and backed by a release liner you peel off. Some high-temperature products use butyl or other specialized adhesive compounds instead of standard modified asphalt.
The layers
- Top surface. A polyethylene or similar film, a woven polypropylene fabric for traction, or granules like those on shingles. The surface protects the compound from UV and foot traffic.
- Reinforcement. Some products embed a fiberglass or polyester mat; others rely on the film for strength and tear resistance.
- Adhesive compound. Asphalt modified with rubber-like polymers, commonly SBS (styrene-butadiene-styrene). The polymers keep it flexible in cold weather and tacky enough to bond to the deck and seal around nails.
- Release liner. Silicone-coated paper or plastic, often split down the middle so you can peel half at a time.
Why the makeup matters
- Self-sealing. The soft compound closes around nail shanks, which is what keeps it watertight under shingles.
- Temperature range. Standard compounds soften in high heat; high-temperature formulas are made for metal roofs.
- Cold application. The compound's stiffness sets the minimum application temperature.
- Compatibility. Asphalt compounds can react with some plastics and sealants, which is why manufacturers list compatible products.
Not the same as
Felt, which is asphalt-saturated paper, and synthetic underlayment, a woven or spun polymer sheet, are mechanically fastened and do not seal around nails. See synthetic underlayment vs felt and ice and water shield in Georgia.