Butong is made using Portland cement concrete incorporating a titanium dioxide powder which has the property of reacting in a photocatalytic way with NOx fumes from traffic. The reduction in Nox can be very significant as shown in demonstration projects around the world in other product uses. Butong is the first panel system using this technology. The unique form of the panel comes from the use of bubblewrap formliner against which the wet concrete mix is squeezed. By using the bubbleshapes in this way the use of materials is significantly reduced compared with flat panels. The dimples also greatly increase the area over which the photocatalytic reaction takes place. The developers have taken it further by incorporating plants in green wall designs - twin panels with compost between them have holes punched in and plants threaded through. Future plans include use of zero carbon cement and use in improving internal environments.