This is a full-body Onyx unisuit by Thrunic who created the Onyx design. They write:
A new Onyx full-body unisuit. It’s got a hood, long sleeves with thumb holes, and long legs. It’s fully lined except for the sleeves. It looks a lot like a wetsuit.
I took it for a test swim in the cool waters around here, and it certainly does confer some warmth, though not nearly as much as a real wetsuit. I think it would work best as a garment for boating or other activities where you’ll both get wet and a lot of sun exposure. It’s not particularly warm when dry, but doesn’t lose much insulation when it gets wet.