Cylindrical composite paperboard cushion core and process for producing same

A cylindrical composite paperboard cushion core comprising:

• (A) a cylindrical paperboard substrate;
• and
• (B) a cushioning layer covering an outer surface of the cylindrical paperboard substrate and comprising at least one expanded paper sheet having a density of 0.1 to 0.4 g/cm.sup.3, said expanded paper sheet having been formed by subjecting an aqueous slurry of a mixture of pulp fibers or pulp-nonpulp mixture fibers containing at least 50% by weight of pulp with a plurality of expansible microcapsules in an amount of 1 to 40% by weight based on the weight of the pulp fibers, said microcapsules each having a volatile liquid core enclosed in a thermoplastic resin shell and capable of starting an expansion at a temperature of from 80.degree. C. to 200.degree. C. to a paper-forming procedure, and heating the resultant paper sheet at the expansion starting temperature of the microcapsules or higher to cause the paper sheet to be expanded.