European Respiratory society disagrees on the cancer risk fwiw https://www.ersnet.org/wp-content/uploads/2022/02/Update-on-... but yeah obviously degraded foam isn't good. The foam isn't actually a required part, it's just for sound reduction.

But I think that proves my point, the supposedly "rigorous" FDA review didn't flag concerns about foam in the airpath of something you breathe through, so what exactly is the approval process buying you? Philips issued a voluntary recall but resmed uses foam in their units too, and while they claim it's a different type of foam it seems there are better ways to engineer sound reduction than putting foam in the air channel and potentially breathing in microplastics.