Such insulation was referred to as "clothing" and usually was made of plaster, felt or even lamp-black, a fine carbon powder. These "modern" insulating materials had replaced "hair felt," a covering made from cattle hair. "It was found to have one serious defect — under the action of heat, vermin bred rapidly in this material."

From: Air Conditioning, Heating & Refrigeration News | Date: 11/12/2001 | Author: Bernard Nagengast