Energy Suspension 4.6101R Rear Spring Isolator Durability is superior for cars, trucks and SUVs; road salt, oil, and a host of other common under car contaminants will eventually destroy the rubber bushings on your vehicles, not to mention the weight and torque forces that typically compress rubber Hyper-Flex replacement polyurethane components stand up well to contaminants that often destroy rubber and have been engineered to give longer-lasting performance and not compress permanently Hyper-Flex is offered in a variety of durometers (firmness or softness), depending on product application; performance tested and race proven; used for all of Energy Suspension products that require a higher level of performance and durability If you are modifying, building a new vehicle for scratch or restoring an old one, Energy Suspension's Hyper-Flex performance polyurethane should be the 'ground zero' focus of your present and next vehicle plans Over two decades of in-house experience in innovating, engineering and formulating wide selection of polyurethane components for many different industries, Energy Suspension has qualified as premier manufacturer of the high quality polyurethane products