We have a few cat hammocks up in the catio, both inside and outside. Izzy loves the inside nap spots, and recently jumped up to the outside sling, probably just to establish that she can. She only gets free roaming of the back yard under supervision, mainly because she runs up trees and gets stuck. The hammocks are made of a double layer of outdoor fabric, with ties on each corner and a grommet in the center. We learned early that the fabric will hold water, so the grommet lets the rain drain and the bed dry out faster. (Side note, an easy way to sew in the ties is to tuck them inside when sewing the two layers with right sides together, like you would for a pillow with lace or piping. Leave a gap, turn the hammock right side out, then reinforce the edge and ties by stitching around again.)