Unlike commercial 3D printers that use lasers, high speed sintering (HSS) marks the shape of the part onto powdered plastic using heat-sensitive ink, which is then activated by an infra-red lamp to melt the powder layer by layer and so build up the 3D part. Researchers from the UK’s University of Sheffield have discovered they can control the density and strength of the final product by printing the ink at different shades of grey and that the best results are achieved by using less ink than is standard. The researchers are able to manipulate the density of the material by up to 40 percent, opening the door to the possibility of 3D printing parts with differing densities at different points. This would enable parts to have greatly reduced weight but equivalent mechanical strength - for example by having a dense outer shell and a lighter inner structure. The ability to maximize strength while reducing weight means the technique would have definite applications in the aerospace and automotive industries.