Abstract: Based on the published literature record, this document provides an overview of the research and development of glass bubbles bulk-fill thermal insulation systems for cryogenic equipment in general and, in particular, for large-scale cryogenic liquid hydrogen (LH2) storage spheres. Glass bubbles (also known as hollow glass microspheres) are used in place of perlite powder which began use in double-wall cryogenic tanks in the 1930s. Included in this overview is a historical summary, a developm…