Chemically speaking, this molecule is "midway" between Sorbitan Oleate and Sorbitan Trioleate, meaning that it's also an attachment of sorbitan (a dehydrated sorbitol (sugar) molecule) with the unsaturated fatty acid Oleic Acid, but inside a ratio of two:3 as a result the "Sesqui" aspect inside the molecule's name. The emollient plant oil coming t