The Gator GR-RACKBAG-4U is a 4U lightweight rack bag with aluminum frame and PE reinforcement. These bags are designed to be a lightweight, portable option to protect your rack-mounted effects processors, rack-mounted bass or guitar amp heads, compressors or EQs and other rack-mountable gear. These bags are sturdy and portable and will stand up to continued use and make them an ideal choice for musicians and recording artists, whether working in the studio or on the go!