AbstractIn the first part the microstructure of polymer melts and semicrystalline bulk material is treated on the basis of the bundle model and with molecular parameters. The meander‐shaped arrangement of the bundles in the amorphous phase can be founded thermo‐dynamically and leads to a radius of the meander of 50 Å. Based on this model a molecular theory of the relaxation processes (α, β, γ) is given and experimentally proved for linear polyethylene. In the last part both limiting cases of the deformation behavior are quantitatively derived in a molecular picture: the ideal plasticity illustrated by the yield stress of linear polyethylene and the ideal para‐elasticity illustrated by the stress‐strain curve of the drawn poly