Any substance which contains active hydrogens capable of reacting with isocyanate will be restricted to very low levels. Specifications for urethane grade solvents typically center on very low water and alcohol contents, typically 0.1% water or less. Glycol ethers also contain active hydrogens and are not suitable for use in urethanes. Historically, esters have contained significant amounts of alcohol. More recently, alcohol free grades of esters have been produced with the designation “Urethane Grade”. The usual quality grades of hydrocarbons and ketones ordinarily are suitable for urethanes, even though they may not be designated specifically as urethane grade.