Which option describes the 'cold flow' phenomenon?

• A. The effects of low temperature gases or liquids flowing in hose or tubing
• B. Impressions left in rubber hose material
• C. Flexibility characteristics of hose materials at low ambient temperatures
• D. Impressions left in natural or synthetic rubber hose material

Answer: (D)

Cold flow is the slow, time-dependent deformation of rubber under sustained stress, even at room temperature. In hoses, this shows up as impressions or indentations in the hose material itself where it has been pressed by clamps, fittings, or internal reinforcement. The defining idea is that the hose material (natural or synthetic rubber) slowly flows or creeps under pressure, leaving visible marks on its surface over time. This is different from the contents moving through the hose (A) or from a general note about flexibility at low temperatures (C), and it’s more specific than just any impression in the material (B) because it specifically describes the material’s own creep under load.