Can I use a home upholstery fabric protector on car seats?

It may work, but results are often weaker. Car seat fabrics are usually made from different fibers, weaves and backings than home upholstery, and they face more friction, sunlight and temperature changes. A protector designed for one may not bond as well or last as long on the other. Products made for automotive fabrics are the safer choice for car seats. Whatever you use, apply it to clean, completely dry fabric and test it first on a hidden area for colorfastness and stiffness.