Aversin and Bavon appear to be similar in action in waterproofing upper leathers; which proofs better seems to depend partly on the leather. If 6% or more of either material is used, the results do not depend much upon the quantity applied. Small amounts of silicone applied with Bavon give no improvement, but small amounts applied with Aversin may. Small amounts of salt in leathers treated with Aversin or Bavon may affect their waterproofness appreciably, but the effects are not neccessarily harmful, as they generally are in silione treated leathers. As regards waterproofing, the finish may be applied before or after Aversin or Bavon. The finishes do not themselves give waterproofness, but can greatly enhance the proofing given by Aversin or Bavon: in the present work, an acrylate finish was better than butadiene. If a salt solution is used in place of water in flexing tests of waterproofness, the results are little changed, but the presence of wetting agents causes considerable reduction of penetration times; the effect of these agents is probably greater for silicone treated leathers, and the wetting agents appear more effective in water than when applied to the leathers beforehand. Although salt which is added to a silicone treated leather always greatly reduces its waterproofness, salt present in the leather before silicone treatment is relatively harmless, presumably because the salt crystals become coated with a film of water repelling silicone.