That’s where 3D printing has a niche.”So how, exactly, does a 3D printer work? With 3D printing, there’s a third dimension: height. The files you feed into 3D printers are 3D images that a software program then slices into horizontal layers. The second most popular method for 3D printing is an older technique called stereolithography, or SLA. Another common 3D printing method is polyjet printing, which allows engineers to work with a wide array of nozzles and materials (from hard to soft) in one print.