Glass on top of heated bed- is Borosilicate necessary? (2 replies)

I'm currently planning a Prusa Mendel build (to be converted into an Open Hybrid Mendel once I get it printing).

I was wondering if it is important that I use borosilicate glass, like Pyrex, on top of a PCB heated bed or if I can get away with using normal window glass. I'm worried about cracking from thermal shock or any other problems that might be caused by thermal expansion. Is there noticeable warping with window glass around ~110C?

I already have a sheet of 8x8 in glass from an unused picture frame, roughly 3mm thick. Is this suitable?

Also, where do you purchase your glass plates?

I apologize if these questions have already been answered. I have been having a hard time searching for them.

Thanks.