A better idea
They melt a lot quicker if you put them through a blender first. Don’t use the household blender. Buy one for the garage. I have one which stays with my garage clothes iron, my garage kettle, my garage microwave oven, my garage food mixer and my garage washing machine.
Anyway. The bloken up granules melt more quickly. Be careful when squeezing the boiling water out of them.
I find the finished result is more flexable than the branded polymorph.