Powerful pain relief. Air activated,continuous heat that lasts up to 8 hours. Rub a535 proheat for back & hipprovides soothing, deep penetrating heat directly where it is needed for up to 8 hours. Odourless. Comfortable.available in small/med and large/xl. Rub a535 proheat for neck, shoulder and wristcontinuous heat therapy providing deep muscle relief.