PCB heated bed. I'm working on this idea for nearly two months, inspired by http://www.neufeld.newton.ks.us/electronics/?p=864 .

UPDATE

tested at 110W and its working flawlesly, gives 108°C in few mins
Now I'm working on great mounting solution

This is V4

• 22x20cm hated area
• you can select what resistance you want 1.3ohms (110W at 12V) or 21ohms
• you dont need any steel or aluminium on top, just plane kapton tape

(I'm testing it at 21ohms setup with 55V PSU which gives me 144W and about 110-120°C, will test with 12V soon and I'll give a report)

etch it on FR4 35um copper board, should cost about $20 or if you are interested email me I can probably etch some for you. Not tinning or copper plating, this would lower the resistance.

There are 4 resistors on the board, final resistance depends how you connect them by solder bridges. Parallel -> 1.3ohms. Serial -> 21ohms.