Electrowarmth as a business has been manufacturing heated mattress pads right here in Danville Ohio since 1939. Made in USA The business was purchased from the Crise brothers in 1997 by the Grindleâ€™s. The Crise brothers were the sons of the original inventor of the heated mattress. The Grindleâ€™s have made many improvements since that purchase in 1997. Two of the most dramatic changes were making most of our units fitted and making all but our 12V units ETL approved.