Because the strength of the doors and windows processed by PVC profiles is not enough, steel is usually added to the cavity to enhance the firmness of the doors and windows, so the plastic doors and windows made of steel inside the profile are usually called plastic steel doors and windows. With the widespread use of plastic steel doors and windows, the PVC profiles used to make plastic steel doors and windows are commonly called plastic steel profiles. Plastic steel is also a common material for guardrails.