POLYMER RESIN

Provided is a resin composition comprising a polymer that is capable of affording a heat storage material superior in humidity permeability and shape retention after phase transition and that is superior in molding processability, namely, a polymer including constitutional units (A) derived from ethylene, constitutional units (B) represented by a specified formula, and optionally including constitutional units (C) represented by a specified formula, wherein where the total number of the units (A), the units (B), and the units (C) is 100%, the number of the units (A) accounts for 70% to 99%, the total number of the units (B) and the units (C) accounts for 1% by weight to 30% by weight, and where the total number of the units (B) and the units (C) is 100%, the number of the units (B) accounts for 1% to 100% and the number of the units (C) accounts for 0% to 99%.