Imperial Pools Nexus NSS016 18' Interior and Exterior Straight Stairs with Polymer Open Top and 2' Radius. Whatever you want your pool entrance system to be, Imperial has the right one for you. Our steps are the most aesthetically pleasing in the industry, constructed with comfort, durability, strength, and safety in mind, and protected with a Limited Lifetime Warranty. Our vinyl-covered open-top Polymer and Steel Stair Systems extend the pattern of your pool's interior finish onto your steps, creating an uninterrupted, continual, elegant look.