Abstract: A paper or plastic surface material of appropriate thickness and stiffness which can be coated with or laminated to asphaltic or non-asphaltic adhesives. The surface material can have a plurality of individual slits formed in substantially parallel spaced rows extending transversely from one end to the opposing end of the surface material. The flexible surface material is expandable by extending the opposing ends of the surface material whereby the slits form an array of openings. The length, width and spacing of the cuts can be varied to achieve desired stretch ratios. The surface material can be easily stored in the non-expandable position and easily expanded to be stretchable and conformable around windows, skylights or other suitable uses.