401 Arctic Seal is a specially designed and manufactured, self-adhering, Flexor SBS polymer modified asphalt underlayment for use on steep slopes to prevent moisture intrusion from ice dams and wind-driven rain, as required by many building codes. Arctic Seal is approved for use under fire-rated, code-compliant roof coverings. Arctic Seal serves a dual role as a flashing membrane, helping protect areas susceptible to leaks such as valleys, roof-to-wall transitions, and around vents and skylights.