  Radio absorptive materials (RAMs) are key elements for receivers in the
millimeter-wave range. For astronomical applications, cryogenic receivers are
widely used to achieve a high-sensitivity. These cryogenic receivers, in
particular the receivers for the cosmic microwave background, require that the
RAM has low surface reflectance ($\lesssim 1\%$) in a wide frequency range
(20--300 GHz) to minimize the undesired stray light to detectors. We develop a
RAM that satisfies this requirement based on a production technology using a
3D-printed mold (named as RAM-3pm). This method allows us to shape periodic
surface structures to achieve a low reflectance. A wide range of choices for
the absorptive materials is an advantage. We survey the best material for the
RAM-3pm. We measure the index of refraction ($n$) and the extinction
coefficient ($\kappa$) at liquid nitrogen temperature as well as at room
temperature of 17 materials. We also measure the reflectance at the room
temperature for the selected materials. The mixture of an epoxy adhesive
(STYCAST-2850FT) and a carbon fiber (K223HE) achieves the best performance. We
estimate the optical performance at the liquid nitrogen temperature by a
simulation based on the measured $n$ and $\kappa$. The RAM-3pm made with this
material satisfies the requirement except at the lower edge of the frequency
range ($\sim$20 GHz). We also estimate the reflectance of a larger pyramidal
structure on the surface. We find a design to satisfy our requirement.
