Custom Hard Foam for the NANUK 909 8-Knife Case Hard Case. Made of high-quality polyurethane foam, the multi-layered set of customizable inserts includes a pre-scored removable layer. This layer consists of foam squares that can be removed in various configurations to accommodate the contents of the case. This solution is ideal if you are seeking a quick and easy way to protect and organize your knives. It comes with the eggshell foam that goes in the lid of the case.