These are the oldest and most commonly used. They were adapted from a design used in buggy seats in the 19th Century. This hourglass-shaped wire coil is joined to adjacent coils by small wire spirals called helicals. The open coil design provides good initial support but these coils fatigue more quickly than more technically advanced coil constructions. You'll know this mattress has reached the end of its life when you and your bed partner are experiencing the 'roll together' or you suddenly realize that your mattress feels more like a hammock.
