Bonnell Springs Mattress type, what is it and what are its advantages? Bonnell Springs are the most common type of spring you can find inside your mattress. They are the traditional spring, hour-glass types that are inside your mattress. It’s used to make the lower part of your mattresses as it is a bit uncomfortable to lie on top, so mattresses manufacturers put in foam, feathers, and fillers to make it a comfy bed. It’s: Durable, Provides Equal Support, and Cheap yet made professionally. Choose wisely as you will spend ⅓ of your life sleeping on this mattress; Bonnell Springs or not, F31 carries professionally made mattresses all year long.