its possible you are not pulling the material tight to begin with. as a long time monokote user & strong convert to ultra cote several yeras ago, I have yet to see much problem using Ultracote . the white does after long exposure to strong sun, yellow. you have to, and can , pull on ultracote a lot without too much fear of melt /tearing. the product does not form the gases during heating & is easier to apply. it stops shrinking at about 300 & WILL NOT (according to instructions) shrink more at higher temps.