HRX stands for High Resiliency Extra and is the foundation and base layer from which the entire mattress sits. The layer is commonly referred to as a support layer and aims to provide opposing pressure that pushes and flexes against your body, contouring to each of your movements while helping to ensure your back and neck are properly aligned to best allow for the ultimate in pressure relief. the result is a super supportive layer that enhances rest and recovery regardless of whether you are a back sleeper or side sleeper.