The big one a new strap attachment version of the largest mtx trunkbag these are the stiffest most weather resistant mtx bags topeak have produced perfect rear rack mount storage bag with side panniers for light mountain touring road touring commuting and errands large capacity expandable main compartment with two large side panniers and a separate top compartment foam walls provide padding and insulation for use as a cooler or camera bag 600 denier polyester dupont teflon coating