Cross-linked ethylenic polymer foam structures and process for making

A process for making a cross-linked ethylenic polymer foam structure, comprising:

• a) forming a foamable melt polymer material by blending and heating a decomposable chemical blowing agent and an ethylenic polymer material comprising a substantially linear ethylenic polymer having:
• i) a melt flow ratio, I.sub.10 /I.sub.2, .gtoreq.5.63;
• ii) a molecular weight distribution, M.sub.w /M.sub.n, defined by the equation:
• M.sub.w /M.sub.n .ltoreq.(I.sub.10 /I.sub.2)-4.63;
• and
• iii) a critical shear rate at onset of surface melt fracture of at least 50 percent greater than the critical shear rate at the onset of surface melt fracture of a linear ethylenic polymer having about the same I.sub.2 and M.sub.w /M.sub.n ;
• b) inducing cross-linking in the foamable melt polymer material;
• and
• c) expanding the foamable melt polymer material by exposing it to an elevated temperature to form the foam structure.