Bonnell coils are a type of innerspring mattress support system. They consist of hourglass-shaped coils that are interconnected, providing a stable and supportive base. This design allows for even weight distribution, which can enhance comfort and reduce pressure points. These coils are commonly used in budget-friendly mattresses due to their affordability and durability. While they may not offer the same level of contouring as other coil systems, such as pocket coils, Bonnell coils are still a popular choice for those seeking a traditional mattress feel.