7" X 8" flexible urethane that was cast from a laser etched piece.  These could be sewn onto fabric as a patch- try to space the thread far enough from the edge so that it doesnt rip the material with flexing. You could also adhere it to fabric using Black Panther from smooth-on- roughen the back of the patch before gluing. There may be less expensive flexible urethane adhesives out there but this is the brand that works the best for me.

Each one will turn from dark purple to pink with heat! They also smell just a bit like apples because I tried out some scent additive for fun.

D is cheaper because it was an experiment with reflective microbeads, not sure it was  a success! It will shift from pale lilac to a dingy pink with heat.

Prices also vary due to more bubbles/imperfections in the casts.