Each panel has 2 meters of carbon tape connected in parallel 2x1m and has an independent power button. It takes about 3A under 12V (36W) for each one or 72W together.
You can sew wire to carbon tape to make a good and flexible connection. The contact place shouldn't be hotter than the tape itself. If not you must increase the contact area. Sewed contact is very flexible.
On each panel sewn 4 pieces of Velcro . Now I can combine them into a single heated vest . A bit like a bulletproof vest. It's very soft and thin. Due to Velcro this vest will be comfortable to wear for a big man or a small woman. Each panel can be used independently with any clothes.
On the inner surface of conventional jackets I sewed 4 pieces of Velcro.
Now I can at any time fix the heating panel on the jacket and make it a heated jacket. It is fully warmed up to 40 degrees in less than one minute.
I love this idea! You can get the tape from hardware store (i.e. Lowes or Home Depot). It's pipe electrical heater tape. It plugs into a power source. You only need to be concerned with core temperature around the heart. You don't need to worry about back or extremities. Your heart will carry the heat throughout your body. You don't need it too hot either. I think affecting your core temp by 7 degrees (F) will be noticeable to the user. Don't want to go too high and be hyperthermic. Some sort of thermistor regulator would be good. You could power it with a lawn tractor battery carried in a fanny pack. If you could get a hold of some flexible solar cells (i.e. nanosolar) or a small Harbor Freight solar cell you could recharge this in the field by standing in the sun for awhile. I've seen a similar idea from Sharper Image with a unit around the neck (uses the Carotid arteries for thermal conveyance).
Keep up the good work! I'm giving you a skull...