Treatment with acid solution of iodate or chlorate increases the rate of felting of wool in soap solution by about 30%. Reagents used for carroting rabbit fur, such as mercuric nitrate in nitric acid, peracetic acid, or alkaline thioglycolate, increase felting rate but cause severe damage. Acid and alkaline peroxide, acid chlorine, hypochlorite at pH 8, ethanolic sodium hydroxide, persulfate, and acid bromated can all produce a small increase in felting rate under mild conditions of treatment but more sever treatment decreases the felting rate. Permanganate/saturate salt, permanganate/water, permanganate/hypochlorite, and permonosulfuric acid treatments do not give increased felting rate under any conditions. The best treatments found for increasing felting are those with acid iodate or chlorate, but these would be too expensive, for the limited increase in felting rate obtained, to be useful industrially. Increased felting appears to be due to weakening of fibers by extensive reaction of the reagent with cortex rather than to changes in frictional properties. Decreased felting seems logically to be due to reaction with cuticle, but a large decrease in felting rate can be obtained with a relatively small change in the difference between anti- and with-scale frictional coefficients (0.29 to 0.22), as measured by the capstan method. Reaction does not have to be confined to, or concentrated at, the surface of fibers to decrease felting rate. All that is necessary is that a sufficient degree of modification of cuticle be obtained, with or without extensive modification of cortex. Industrially useful shrinkproofing reagents are those which are sufficiently reactive to give cuticle modification when low concentrations are used and thus when all-over reaction and damage are correspondingly low.