Steaming the foam might seem a bit more obvious once you understand the concept, but steaming the upholstery is actually the most effective “trick” used in the upholstery trade to get great fitment with leather and vinyl interiors. Steam is unique in that it applies a “wet heat.” Most of the time, the application of heat to anything will dry out that substance. This is the key to why steam is so effective in working with leather and vinyl. Both leather and vinyl will relax and become much more malleable with the application of heat. However, leather is very susceptible to drying out if heat is applied directly. Vinyl is just less susceptible to heat, but if enough heat is applied, then the vinyl could melt. This is why steam is the key. It applies a “wet heat,” which allows both the vinyl and leather to heat up to a temperature that makes them easier to manipulate without having them dry out or melt so quickly. However, the heat from the steam can still dry out the leather or damage the vinyl if left in the same spot too long.
So, it is very important to apply the steam to the inside of the upholstery so that it is not directly against the leather and to keep the steam moving around inside the cover. This will heat the upholstery evenly and at the same time keep the steam from damaging and specific parts of the upholstery. After you steam the upholstery, it will become extremely malleable and much easier to adjust and place properly to help accomplish a wrinkle-free install.