How does the heat-transfer vinyl process vary from sublimation?

Similarities: Both sublimation and heat transfer vinyl (HTV) are processes used to decorate onto soft substrates, like garments, and both processes utilize a heat press to adhere to those garments. 

Differences: HTV is a film that has a clear plastic carrier sheet on the front. HTV can be used to decorate fabrics by using a plotter cutter to cut your design into the back side of the vinyl, remove the excess vinyl away from the design (this process is referred to as weeding), and then you place your design onto the garment and heat press it for the recommended time. As the vinyl heats up the glue, it activates on the back side of the vinyl, adhering it to the garment. Sublimation uses a translucent dye/ink that is printed onto a transfer sheet through an inkjet printer. For garments, the design is printed in reverse so that when transferred to the garment, the design will have the correct orientation. When the sublimation transfer heats up in your heat press, the sublimatable ink turns into a gas and molecularly bonds to the fibers of the garment. The sublimatable ink can only bond to polyester and, because it is semi-translucent, you are not only limited to the blend of shirt but the color of the shirt as well. You can use a cotton-poly blend but the higher the poly content, the brighter your design.

HTV is more versatile in the sense that it has an adhesive on the back of it that activates under heat. This means that it bonds onto the top of the garment, allowing it to go onto any color and just about any blend of shirt, but it does have a heavier feel than a sublimated shirt.

   —JDS Industries