In a recent order from ECF I bought one of these (actually I bought two but this is the one on question)http://www.equinecaninefeline.com/catalog/design-mini-igloo-hamsters-mice-blue-cotton-p-1221.html
I gave it to my boys the other day, and noticed this morning that they have industriously chewed out the inside layer at the back, and filled the bottom of their cage with tiny little foamy bits :(
I'm not entirely happy that they are mouse safe so I've cleared it all out and removed the igloo, but just thought I would post to say that I wouldn't recommend them for known chewers!
I think they will be ok for my girls, because they don't deconstruct hammocky things in the same way as the boys!!