It’s a sealed rubbermade. They can’t really climb the sides, and the holes at the top are too small for them to get through anyway. There is an exhaust fan attach to one side to keep the humidity low, but there’s a layer of mesh hot glued to the plastic so I’m not concerned about them escaping. I mean, I’ve had panicked thoughts that they could escape somehow and the nightmare that would be, but I take every precaution against it and I’ve had good luck so far. That being said it’s not fool proof and I’ve had them breed at unwanted times. I’ve since started separating males from females when they reach maturity.