The permeation and diffusion of H2 and D2 through Rodar (an Fe−Ni−Co alloy), and the permeation of D2 through Niromet−42 (an Fe−Ni alloy) have been measured by a membrane permeation technique. In the range of 180−550°C, the coefficients for Rodar are: KH2 = 4.9×10−3 exp(−13500/RT) cm3 (STP) sec−1 cm−1 atm−1/2, DH2 = 6.3×10−3 exp(−11100/RT) cm2 sec−1, KD2 = 4.8×10−3 exp(−13900/RT), DD2 = 2.6×10−3 exp(−10300/RT), and for Niromet KD2 = 3.4×10−3 exp(−13600/RT), where R = 1.987 cal mole−1 deg−1. Deuterium permeability measurements indicate that coatings of tin or tin−lead solder are very effective permeation barriers. At temperatures below 170°C, either coating has a permeability that is approximately five orders of magnitude less than an equivalent thickness of Rodar. However, conventional application of solder with an organic flux will injet ∠5×10−4 cm3 (STP) of hydrogen/cm2 of soldered Rodar. Dependent on the thermal environment, the injected hydrogen can diffuse through the Rodar and react with available oxygen to form water.