I can vouch for their sturdiness. I had them holding my bioactive enclosures, which weighed a ton, for a while. I was always afraid that if I sneezed in the wrong direction they’d give way, which is why I switched to heavy duty shelving. After having them banging around in the garage and a couple were even outside for some time, I currently have them back in use and they’ve survived my abuse just fine. The shelf on the bottom isn’t terribly sturdy, but the frame itself is.