A vacuum mattress, or vacmat, is a medical device used for the immobilisation of patients, especially in case of a vertebra, pelvis or limb trauma (especially for femur trauma). It is also used for manual transportation of patients for short distances (it replaces the stretcher). It was invented by Loed and Haederlé, who called it "shell" mattress (matelas coquille in French). It consists of a sealed polymer bag (bigger than an adult human body) that encloses small polystyrene balls, with a valve, straps and handles. It is washable and invisible to X-rays.