4 strong polyurethane wheels with stainless steel bearings. Large 2-person fold down handles. Watertight, crushproof, and dustproof. Automatic Pressure Equalization Valve - balances interior pressure, keeps water out. Easy open Double Throw latches. O-ring seal. Open cell core with solid wall design - strong, light weight. Retractable extension handle. Stainless steel padlock protectors.