Thermal wrap. I put one on my lower back last night due to an ache. I had an organised ride this morning so I slipped the wrap (still giving out heat) halfway up my back and went for the ride. I've just got home 14.5 hours later it's still giving out heat.
I can see myself using one of these on long winter rides, it's very comforting !
https://www.landysch...AiABEgJ7BvD_BwE