Cold flow refers to the permanent deformation of a cable’s insulation or jacket caused by mechanical pressure or stress, rather than by exposure to heat.
Cold flow is a physical phenomenon that occurs when insulating or jacketing materials, typically polymers or thermoplastics, yield or deform under constant pressure or mechanical load over time. Unlike heat-related softening or melting, cold flow happens at normal or low temperatures and is driven by the long-term application of stress. This deformation can change the physical shape of the insulation, reduce wall thickness, or alter spacing between conductors, which may impact a cable’s dielectric properties or overall integrity.
In the wire and cable industry, understanding and controlling cold flow behavior is critical, especially for cables used in structured wiring, AV systems, and industrial control applications where pressure from binding, bending, or bundling is common. Materials such as polyethylene (PE), polyvinyl chloride (PVC), and fluoropolymers are often engineered with specific formulations to resist cold flow, improving dimensional stability and ensuring consistent electrical performance.
Cold flow resistance is typically evaluated during product design and testing to ensure that the cable maintains its form and function under long-term mechanical stress. This includes examining how insulation behaves under compression, tension, or winding forces. A high-quality insulation compound will recover its shape once stress is removed or maintain structural integrity even under prolonged load.
Performance requirements related to cold flow are generally guided by UL (Underwriters Laboratories) and ICEA (Insulated Cable Engineers Association) standards, which assess insulation durability and mechanical performance.
The term cold flow originated in materials science during the early development of polymer-based insulation in the mid-20th century. As plastics began replacing rubber and paper insulations, engineers observed that some thermoplastic materials exhibited time-dependent deformation under load. This discovery led to the formulation of improved compounds with better mechanical stability and the establishment of modern testing methods.