The 4 in 1 Carboy shield is so-called because it has four functions. It can help keep carboy contents warm in cool conditions, cool in overheated conditions, protects the carboy contents from light, and also acts as a padded, protective shield against incidental contact with hard surfaces that can lead to breakage. Stop using a combination of ineffective towels, trash bags, blankets, and packing peanuts! The 4 in 1 Carboy shield can help you cover all your bases with just one padded sleeve! This is for use with standard 5 and 6 gallon carboys only.