A seat shade is a small canopy that attaches directly to an individual chaise or chair, giving one person shade without an umbrella, a pole or a base anywhere on the deck. On a tanning ledge, where there is often nowhere to put a base and no deck to drill, it is frequently the only shade option that works at all.
Seat shades are made to fit specific frames, so order the version that matches your piece. There are separate models for the chaise and chaise deep frames and for the chair. Fitting the wrong one is the only thing that goes wrong here, so confirm your seat model before adding to cart.
The canopy fabric is UV resistant and made to stay outdoors. For broader coverage over a group rather than a single seat, look at cantilever umbrellas and in ground umbrella mounts.