Material: steel is the traditional material; but wood, plastic, or laminate are sometimes used. Plastic or laminate lockers are sometimes advocated in environments, such as near swimming pools, where moisture accumulation may cause steel lockers to rust over time. They can also be used in external applications where internal space is not available.
There is a luggage storage service a short one minute walk from Union Station in downtown Denver - LUGDEN. You can make a reservation online - lugden.com, call - (303) 747-5600, or show up as a walk-in. They offer hourly, day, overnight and weekly bag storage. Great place to store your luggage if you're on a layover from Denver International Airport, or going to a concert, or headed to a Rockies game at Coors field and want to enjoy yourself without having to lug your bags around.