Repti-Racks uses HDPS material in many of their cages. 1/4 inch of that material is much tougher than 1/4 inch of closed-cell expanded PVC. So don't try and compare thickness alone when the material is different from other companies.

Example - 1/8 inch of HDPS (I have a cage made from that) is much stronger than 1/8 inch PVC. In fact, it would likely be impossible to make an effective cage the same size with 1/8 inch PVC.
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Mark