The use of thiourea-formaldehyde resin for retarding the rate of yellow ing of wool by sunlight has been examined. This method provides considerable protection against yellowing, particularly of wet fabrics. It has been found that treatment with thiourea- formaldehyde mixtures. which does not give rise to resin, provides similar protection against yellowing. This modification has the advantages that the handle and color of the wool are unaffected, As for the resin treatment, initial rinsing reduces the pro tective effect, although this is not further reduced by subsequent washing.