Double wall vacuum insulation for all day hot & cold retention. 18/8 stainless steel for highest durability. Dishwasher safe. Lids are compatible throughout all PACKOUTâ„¢ bottles and mugs (not tumblers). Twist and lock mechanism for connectivity with all PACKOUTâ„¢ components. Part of the PACKOUTâ„¢ modular storage system.