A biconic innerspring mattress, also known as a Bonnell innerspring mattress, is a type of mattress that has a core support system made up of biconic springs. These springs, which get their name from their double-cone or hourglass shape, are connected together by a metal wire to form a unified support structure.

The design of biconical springs offers several advantages. First, their unique shape allows for even weight distribution across the mattress, which can help minimize pressure points and provide adequate support to different parts of the body. Additionally, biconical springs have a certain amount of give, meaning they can compress under weight, providing responsive support that adapts to the contours of the sleeper's body.

They are even more durable because the steel springs are strong and hard-wearing, meaning they can maintain their shape and support for many years. Additionally, the open spring system allows for good air circulation, which can help keep the mattress fresh and well-ventilated.

However, it’s important to note that conical spring mattresses may not offer the same level of sleeping independence as other types of mattresses, such as pocket spring mattresses. This means that movement on one part of the mattress may be felt elsewhere, which can be uncomfortable for couples or sleepers who are sensitive to movement.