That's my take on filters and I'm sticking with it.
It is basic science. Objects cannot enter a space that is a vacuum. And filters often turn a pouch into a space of no air at all. So as stool is expelled, it cannot fall into that vacuum.
I'm on an endless quest to find the right gear for my lousy stoma (colostomy), so I've tried samples from many, many companies. There's a picture of my stoma among my profile pics. My earliest gear had no filters. They were two piece so I'd just burp the pouch by opening the stoma hatch at the top. Never had any pancaking whatsoever. So during the day I cover the filter with a sticker and remove that sticker while sleeping.
My stoma nurse ordered pouches with filters. Automatic pancaking on those pouches devoid of air. So I'd have to get air into the pouch by allowing some in from the emptying door at the bottom. Pancaking would stop.
That's my story and I'm sticking with it. And I still haven't found the right gear. Not for lack of trying. It's at the point where if there's stool on "just" the convex part of the base after two days that's a big win. I'm changing my stuff every 2-3 days now to maintain skin health until a more sustainable option appears.
This is Quite depressing.