Short answer: what it can be applied to and how it feels.
Long answer: Our Varsity formula can be applied to 100% polyester, 50/50 or 100% cotton fabrics. And since the Varsity formula contains a dye-blocking additive, it is opaque on most dark colors. It also has a more durable feel.
The Classic formula will only apply to 100% cotton and 50/50 fabrics. Classic applies at a hotter temperature, so it cannot be applied to Polyester fabrics. It feels softer.
Click here to find out which formula will work best for your next project.