The BrewBuilt Neoprene Carboy Sleeve works great for maintaining the internal temperature of your 5, 6, or 6.5 gallon glass carboy. Highly recommended for use with the BrewBuilt Carboy CoolStix. The added insulation will lower the amount of cycles needed to maintain fermentation temperatures and greatly assist in cold crashing. The sleeves are 6 mm thick with stitched piping on the edges for exceptional durability.