Viewer Challenge - Water cooled Blanket

That's a really cool idea (pun intended). I think the biggest hurdle in a project like that would probably be the hose. Rubber or plastic doesn't conduct heat well enough and metal tubing is inflexible. It probably wouldn't be very comfortable either. You'd also need a material that could withstand the pressure of body weight without obstructing water flow, this most likely would require thicker walls which would compound the issue. Perhaps a sleeping mat instead of a blanket? Using a foam mat (like a yoga mat or a camping sleeping pad) for a base you could use metal tubing with multiple S bends to maximize surface area (think something like a higher frequency sine wave) embedding it in the foam so it's flush. Use metal tape to cover the top of the mat, it's somewhat flexible and will help conduct your body heat into the tubing. Box on the ground could contain the peltiers, the pump, an arduino with a thermistor for heat control, LCD for display, and some buttons for temperature control. Plastic flex tubing links the mat and the box. Peltiers can be set up in a hexagonal pattern cold side out hot side in, use CPU heatsinks inside the hexagon for heat transfer and 2 200mm case fans to provide air flow through the sinks. Metal tubing in a tight wrap can be wound around the outside of the peltiers for heat transfer to be connected to the plastic flex tubing and the pump. Toggle switch to provide switching from cooling to heating. This design still wouldn't be very flexible but you could cut the mat into 6 inch sections and use flex tubing to connect each section together, keeping the S bends to ~4 inches peak to peak, 550 paracord running through all the sections on the left, right and center could help hold it all together, providing increased flexibility and easier storage.

Anyone else have any thoughts?

*To make bends in metal tubing without kinks fill the tubes with a fine grit sand before bending. Your best option for metal tubing would probably be aluminium, copper gives better heat transfer and is more durable but aluminum is cheaper, although if you go with aluminum you'd need to go with an inhibited glycol or dielectric fluid over water. I'd probably go with propylene glycol and water (PGW) as a heat transfer liquid for this application. Your other option is stainless steel, in which case I'd go with deionized water as a heat transfer liquid. Whatever you do don't use tap water! It may be cheap but the impurities can clog your pipe.

I might go the route of no tube. The blanket could be two layers of a type of plastic or rubber, cold water enters one corner and exits the diagonal one. You have something like flexible ribs inside that offer multiple pathways (so they don't all close under bodyweight) and direct the water throughout the blanket.

So it's kind of like being made of ultra flexible tubes with multiple pathways so you can't close them off.

I might go the route of no tube. The blanket could be two layers of a type of plastic or rubber, cold water enters one corner and exits the diagonal one. You have something like flexible ribs inside that offer multiple pathways (so they don't all close under bodyweight) and direct the water throughout the blanket.

So it's kind of like being made of ultra flexible tubes with multiple pathways so you can't close them off.