It was not clear from the description, but this *is* an expandable bag and not just a set of walls. SO, happy to find that there is a bottom to keep items big and small from falling thru the cart bottom. Sturdy material, so I am glad I got this instead of the cart only. Also, more flexible and safe-keeping of items than just a hard bottom add-on. The ONLY caveat is that wide items may not fit inside that would on the raw cart or the hard bottom shelf.