Hose and Coupling Knowledge Base

Q: Why do hoses get stiffer over time?

A: It is true that hoses, particularly those made out of vinyl chloride, can become stiffer with continued use. Vinyl chloride resin is ordinarily a hard material often used in pipes.

To make it soft for use in hoses and cable coverings, a plasticizer is introduced during the manufacturing process. No chemical reaction is involved. Instead, the plasticizer molecules situate themselves between the vinyl chloride molecules, providing a soft cushion for flexibility.

This graphic illustrates how external stimuli such as ultraviolet light and heat can cause the plasticizers to liquefy and move to the surface in a phenomenon known as plasticizer migration. When this occurs, the surface becomes sticky, a sign that the plasticizers inside the hose material are decreasing, which will lead to increased stiffness.