If you want to make bulk substrate that you can't pasteurize, these bags will survive a pressure cook. Just fill it up with your mix, seal it up, and cook away. The bags will come out still sealed and intact and; once cooled down, ready to be mixed with your favorite spawn to be colonized. I tossed these bags in with my second order through MMM and mailed the mushroom man a certified envelope full of cash. I go this option because who doesn't love freebies? I assure you it's legit. Nobody gains this level of recommendation on Reddit or the shroomery forums if they ain't for real.