Metal hoses can withstand very cold and very hot temperatures, both in the surrounding environment and in the material going through the hose. They also resist vibration, abrasion, and many chemicals and will not allow gas to permeate through the hose wall. These hoses are sometimes used as an outer cover for other hoses to protect them from abrasion and overbending. They keep their shape and will not collapse when under a full vacuum. Interlocked metal hoses are made from a single strip of metal that is profiled and locked onto itself. The hoses' overlapping sections can slide back and forth to allow the hoses to flex. Corrugated metal hoses (also known as jacketed hoses) are used for conveying products that need to be heated or cooled during transfer. They have a flexible inner metal hose enclosed in a flexible metal outer hose (or jacket), and they have fittings on their ends that stop any material being conveyed through one of the hoses from moving into the other hose.