My friend would like to sew a lightweight cat harness. Her cat is going to have surgery this summer on both hips and knees (not all at the same time). She’s a little over one year old. My friend would like something lightweight so the kitty does not overheat. She was thinking some kind of ribbon, but I said I would ask on here to see what people suggested.
If it’s just going to be straps, narrow (1/2-3/4" wide) nylon strapping would be ideal, and would not be hot.
If there will be solid parts, maybe use nylon mesh; a laundry bag could be repurposed. Dollar Tree has small ones 3/$1.25, great deal. I use them to store scraps, ribbons, and embroidery floss.