Probably as what's it's designed for. And after hideys are placed in it. But I think that's just a shadow of the top bars. I couldn't find a bar space measurement for safe-as-adult-cage, because all I found was safe-for-babies-cage measurement. Does no one know how big a space just fits an adult rat's head?If their head can fit, their body can fit too. I would also recommend a different carrier... Also, I think all the open space/nowhere to hide can make rats very stressed. The carrier looks like it has wire bottoms? Very bad for their feet. What are you using this for?