conveyor material - 24" wide and if you find the right place to pick it up from they will give you the drops they have. I walked out of one place with 50' of material. PITA cutting 1/4" rubber mat, but it keeps everything in its place. If there is half of a chance of using one of my boxes as a temporary road box that is what I set it up with. For the toolboxes that stay at my shop or at home I pick up the material from sears designed for that. I think it's about 3/8" thick and way easier to trace and cut tool outlines in. That stuff is the **** especially if your drawer has a lot of heavy gear in the front and light stuff in the back. It helps to keep it all separated, but it does fold up over time.
An old timer turned me onto the conveyor material when I was an apprentice with the ironworkers local. The other stuff I came across when I was window shopping one day.