Are FDM parts completely solid? What infill do you use?

Parts that come off the FDM printer are mostly not solid. There are a few layers of solid material on the top and bottom of the part, called roof and floor layers. There are also a few solid layers on the sides of the part, called walls. Inside this is a lattice structure, which is called the infill. We make default 50% infill on all the FDM plastics except TPU, which is a default 15% infill.

For higher or other specified infill percentage is also supported, but the build time or price can be different.