Dual layer heat shrink tubing

A dual layer heat shrink tube comprising:

• an inner polymeric layer consisting essentially of PFA, FEP, EFEP, or PVDF and, optionally, one or more pigments, dyes, or fillers, with a thickness t1 and an outer diameter D1;
• and
• an outer, expanded polymeric layer consisting essentially of PTFE, FEP, PFA, PEEK, or PVDF with a thickness t2′ and an outer diameter D2′ obtained by expanding a polymer tube from D2 to D2′ and t2 to t2′ at a selected temperature so that D2′−2(t2′)>D1,
• wherein a ring cut from a cross-section of the dual layer heat shrink tube, slit into a rectangle and gripped at cut ends by tension grips within a DMA, and subjected to a temperature sweep of 3° C./min at a frequency of 1 Hz from the onset of a melting endotherm of the inner polymeric layer (as determined by DSC) up to the onset of a melting endotherm of the outer, expanded polymeric layer (as determined by DSC) has an area under a tan δ curve that is greater than 1° C. and less than 12° C.