What's the difference between the colored Trizact belts and Grey Trizact belts?

3M makes several different Trizact structures for different uses. The colored Trizact belts in Green, Blue, and Orange are the 272LA model of Trizact that has been around for decades. 

The 272LA Trizact material is on a thinner backing material and will generate more heat on the glass as you work. They require a little more pressure to adequately work the surface on your glass and you need to be careful to have enough water and not to overheat your glass as you work on them.

Due to these detriments, 3M formulated a new Trizact material called 237AA. This is the grayish brown colored Trizact belt.

The 237AA belts have a cloth backing to them so they track easier on your belt sander. The added cushion of the cloth backing also means you don't have to apply as much pressure to the belt in order to get them to grind efficiently. In fact, if you apply too much pressure to the 237AA belts you can prematurely wear them out. They also do not generate as much heat as the 272LA belts do. They will still generate more heat on your glass than a typical silicon carbide belt, but not as much as the previous colored Trizact material.