Once you snap the frame on (see the yellow one in the photo), the lid screws on and off. They are airtight and leak-proof as well as EXTREMELY sturdy. I sit on mine all the time. These make the BEST containers for storing feed and for bringing feed on the road.
I bought a bunch of those orange "paint" buckets at Home Depot and snapped the lids on. I keep one in the trailer for feed and cookies that goes with me for lessons and shows. The others are in my tack room for grain, beet pulp, and rice bran. And the best part about them is that they keep out bugs and rodents!