He then inserted a piece of carbon filter pad that he cut to fit inside the hair- dryer. He used the original heat shield to hold the filter in place, but suggests that you can instead use a roll of cardboard, or something else to keep the filter to the back of the hair-dryer. That’s really all there is to it.
He then reassembled the hair-dryer and connected it to a 7.2V 3800mAh NiMH rechargeable battery pack using some electric tape. He had used the switch in his hair-dryer for another project, so he used a connector switch. Andrew’s hair-dyer had diodes around the motor and the switch and, if yours have them too, he recommends you unsolder them.