It is more about the hole size not the overall rigidity. Even if it flops it could be problematic. can you get some pics?I've actually seen a difference in window screen both labeled as polimer at the hardware store. Some is like a fabric, it flops and folds and doesnt bend. And some is like metal, its hard, solid, and actually bends when I move it instead of just flopping around. I use the one thats more like fabric in my enclosures and havent had a problem so far.
As for net cages, how do you guys go about furnishing them? Im guessing you dont glue anything to it. What about the substrate?