Microstructural characterization of helium bubble distributions is provided for a series of palladium foils that were injected with 3He under varying conditions of dose, temperature and starting foil condition. Specimens were prepared in cross section and bubble layers ∼500 nm thick are found starting ∼300 nm from foil surfaces. Bubble densities and sizes were found to vary with foil microstructure and injection conditions, with larger bubbles formed on microstructural features such as sub-grain boundaries and nearer the surface. Most surprisingly, bubble sizes are found to be as small as 1 to 2 nm in diameter. Specimen preparation details and imaging issues for very small bubbles are discussed.