This particular market is developing rapidly. There will always be new products coming out so we suggest that you do some decent research before taking the step. The government websites, Energywise or BRANZ (the independent and impartial research, testing, consulting and information company providing services and resources for the building industry) or WANZ Window Association of NZ provide extensive information and research. Of course here at Wanaka Joinery and Glass we are here to help with advice and guidance on your existing Wooden Windows!!