For years, pre-heating was recommended as a first step to ensuring successful application of heat printing on garments. This helped eliminate wrinkles and remove any moisture from the apparel that might interfere with adhesion, especially with cotton. Today, many garments being sold are made from synthetic fabrics.
These fabrics don’t wrinkle like cotton might and are also moisture wicking so they don’t hold moisture like a natural fabric will. Unless you are heat printing on cotton or other natural fabrics, you can skip this step and save time in the production process.