The invention describes powders for use in the production of spatial structures, i.e. molded bodies, using layer build-up methods, as well as methods for their efficient production. The powders have the special feature that they have good flow behavior, for one thing, and at the same time, have such a composition that the molded body that can be produced with the powder, using rapid prototyping, has significantly improved mechanical and/or thermal properties. According to a particularly advantageous embodiment, the powder has a first component that is present in the form of essentially spherical powder particles, which is formed by a matrix material, and at least one further component in the form of stiffening and/or reinforcing fibers, which are preferably embedded in the matrix material.