Didecyl polyoxyethyl ammonium borate (DPAB), also known as Polymeric Betaine, was developed as a co-biocide for chromium-free copper based wood preservatives in Europe in the 1980’s. This paper summarizes the properties of DPAB as a wood preservative. Unique properties related to the betaine nature of DPAB are discussed in terms of the structure-property relationship. Physical properties of DPAB treated wood and properties of DPAB formulations are discussed. Unlike many preservative systems which have negative impact on strength and other physical properties of wood composites, it was discovered that DPAB based formulations were especially suitable for treating wood furnish before composite manufacturing. Typical laboratory and field performance data of DPAB formulations are presented.