Looks like high density foam. If so I would expect it to be very durable. You can drive a tuck over some of the better quality stuff and not even compress it. I think I'll get one and try to put a gasket on it or just use cold packs instead of ice. I think it'll be great to keep your sandwiches cold and keep them from getting beat up in the cooler. Doubt this would displace a real cooler on a longer ride though.
Works great with sandwiches and children's juice boxes, which tend to get smashed in the "adult" cooler. I use ice in a quart ziplock and the contents stays cold for about 5-6 hours. Cleanup is a breeze as the bottom section just slides right out. I've been very happy with it and would buy it again.