High quality exterior varnish stains for timber protection are a complex mixture of ingredients carefully chosen and balanced in order to achieve maximum performance. The effect of a number of parameters on durability over a 3-5 year period in the United Kingdom and Florida (USA) have been studied. Results demonstrate the long term advantage to be gained from the use of resins specially developed for exterior varnishes which produce highly extensible coating films. The selection of transparent oxides, waxes, flatting agents and fungicides is also discussed together with the advantages to be gained through the incorporation of controlled thixotropy into the wet varnishes. A number of starting point exterior varnish stain formulations are included. Graphs, photographs, tables, references.