Emulsion design in terms of polymer composition and particle size is discussed. The significance of the glass transition temperature (tg) for paint film formation and subsequent paint film behaviour is discussed. Data are presented showing the variation of tg with copolymer in the case of selected monomer pairs. Exposure to light causes gross-linking and degradation of polymeric binders. Measurement of changes in physical properties such as tensile strength, ultimate elongation tg., etc., during exposure permits predictions to be made concerning exterior durability of paints made with different resin binders. The loss of film thickness during weathering can be used to obtain information on chalk resistance and durability of paints after relatively short periods of outdoor exposure. Chemical especially alkali, resistance depends very largely on copolymer composition. It can be assessed by accelerated tests. The rheology of paints is discussed with particular reference to the particle size of the binder emulsion. The effect to thickeners and dispersants is briefly syrveyed. Graphs, references.