Whoah, its hot outside! Vinyl application has some optimal application temperatures. If it is too cold out the vinyl will become stiff and brittle. The adhesive doesn’t get the chance to adhere properly and will possibly peel off in short order. On the other end of the spectrum, heat can also cause the vinyl to almost melt. It becomes too pliable, the adhesive too soft and aggressive. Application can become a nightmare, or even impossible. Optimal application temperature is no colder than 16 degrees Celsius, don’t forget to take into account wind chill on that surface. As for the heat, it really depends on how large the decal is, thickness and type, or if you are applying in direct sun. If you find the surface you are about to apply the decal is too warm to touch, try to wait until a cooler time of day. (And yes, this is a picture of a slightly melted gooey pile of vinyl, for effect ūüėČ )