GLAVEL is a recycled glass aggregate product out of Vermont that doubled as our gravel layer AND our under-slab insulation. With an R-1.7 per compacted inch, it worked well to provide us the insulation we needed. It was also super easy to lay down. Two of us opened the bags, spread it out with a rake/shovel (well for the first go…then we realized it might be smarter to dump the bags using a machine ;) and then used a compactor to finish it up. This stuff is super light and feels like pumice stone, but once compacted makes a strong structural base. Recycled products make us feel groooovy!