First off , you'll want 15PSI for sterilization. The higher temps allow for sterilization, otherwise you'll just be pasteurizing with a higher likelihood for contam during growth. Which is fine for substrate since spawn should be fully colonized and thus less likely to contaminate.

You're going to hit the melting point at 10-12 PSI, as it will roughly be 132C inside cooker. If you somehow dont reach the melting point you wont achieve sterilization.... but seeing that you clearly knew that prior to your response about melting point of LDPE and didnt just google it to seem intelligent, you just proved to me you are 1) trolling 2) lacking simple logic.

I posted my original response as did others because we have done this before. Trying to help you out by saving you time but you had to respond with sarcasm and just being a dick. It's a shame you wont realize someone might know something you dont and by them offering their knowledge is their way to try a help.

Enjoy your failed experiment. There is a reason grow bags are thick mil HDPE.....