Believe it's acrylic.

I’ve heard of ppl using acrylic based paint to do so.

For my current remodel I'm thinking of getting an American Standard acrylic tub that is deeper, looks nice and is better for soaking in (the Kohler is too low to soak in.).

This is a pilot project between us and the cleaning service.As to your previous question about detailed house rules, we do have detailed clauses about care of the property (e.g. do not use abrasive cleaners on acrylic tubs).

Good news for you cracks in granite can be fixed by filling with an acrylic but remember later you need to re-polish it otherwise the crack will remain easily visible.

http://www.ppgpaints.com/products/pure-performance...It is 100% acrylic, making it more durable than a vinyl acrylic like the Promar 200, with good coverage.  

I did whole house acrylic stucco re-coating.  

Acrylic is easy to clean.

Instead of re-glazing, which is basically a high-tech paint job, and replacing, which involves chopping out the old one and replacing it with a 2-part tub & surround combo (necessary in my homes), a relining is a drop in acrylic shell that's precisely matched to the make and model of the old tub.It's supposed to cost a lot less than a completely new tub (you're not removing the old one) and more of an upgrade than refinishing.

These are usually 1/8"-1/4" thick acrylic shells that drop into your existing tub to 1) cover it up and make it look pretty and 2) eliminate small leaks in the old tub's surface.