In interplanetary travel and high altitude flight, humans will be exposed to high energy charged particles from solar flares and galactic cosmic rays. These particles lose energy in a material by Coulomb interactions and nuclear collisions. In nuclear collisions, large amounts of energy are transferred and secondary particles are formed from both the projectile and the struck nucleus. A significant portion of these particles are neutrons which can only lose energy by collisions or reactions with a nucleus. Hydrogen-containing materials, such as polymers, are most effective in reducing the neutron energy. When reduced to very low energies, neutrons have a high probability of reacting with a nucleus. Such reactions are dangerous in the human body, and can cause electronic equipment failure. Low energy neutrons react particularly well with a stable isotope of boron, 10B. To test structural materials which contain both hydrogen to reduce the energy of neutrons and boron to absorb neutrons of reduced energy, samples of two polyimides were made which contained varying amounts of either amorphous boron powder or boron carbide whiskers. The polymers used were a thermoset, PETI-5 from Imitec, and a thermoplastic, K3B from Fiberite. Both materials were made in pure form and with up to 20% by weight of the boron additives. The addition of boron in either form did not change the thermal properties of these materials significantly. However, the compressive yield strength and the tensile strength were both affected by the addition of the boron materials. A neutron absorption test using a PuBe thermal neutron source showed that a 0.5 cm thick sample of K3B containing 15% amorphous boron powder absorbed over 90% of the incident neutrons.