Abstract: Polymers of C4 olefins having a viscosity of 15 to 35 centistokes at 100.degree. F show improved performance as cosmetic oils, in comparison with squalane. These polymers are prepared by polymerizing (a) isobutylene by itself, or (b) C4 hydrocarbon olefin containing a mixture of at least two of isobutylene, 1-butene, 2-butene and butadiene, using a catalyst; then removing high molecular weight and low molecular weight compounds by distillation; hydrogenating the remainder of the polymerization product; removing carbonyl compounds therefrom if necessary and further purifying the resultant polymer by steam distillation or treating same with activated carbon or solvent extraction, to deodorize same.