A polyol is an alcohol that contains a plurality of hydroxyl groups, and includes diols such as the glycols (dihydric alcohols) ethylene glycol, propylene glycol and trimethylene glycol; triols such as glycerin (1,2,3-propanetriol); esters of hydroxyl-containing binders also may be used, with mono- and diesters of glycerin, such as monoglycerides and diglycerides, being especially preferred; and p