United Asphalt manufactures various underlayments.

United Glass Base Sheet is a fiberglass mat coated with Type IV asphalt. Glass Base Sheet is used as the base ply in hot, cold and torch applied built-up and modified bitumen roofing applications.
Data Sheet

United Ply 4 Felt is a fiberglass mat saturated with TYPE IV asphalt. Ply 4 Felt is a ply sheet used in BURA hot mopped roofing applications.

United Ice and Water Protector is a Self-Adhering & Skid Resistant granulated shingle underlayment which is used on eaves, valleys, ridges, dormers and skylights. United Ice & Water Protector is used to protect roofing structures from water penetration caused by ice dams and wind driven rain.
Data Sheet

United High Temperature Ice and Water Protector is used under standing seam metal roofing, metal shingles and metal roof panels. This protects roofing structures from water penetration caused by ice dams and wind driven rain.