Bonnell Coils Bonnell Coil System, Image from Bedrooms & More, Seattle, Washington The oldest type of coil used in mattresses is the Bonnell coil. Bonnell coil mattresses are often called "traditional mattresses" or "traditional innerspring mattresses." Other types of coils have been developed since, but they all originate in the Bonnell coil. Bonnell coils themselves were developed from buggy seat springs. They are hourglass shaped. The ends are knotted, the end of the wire...