A storage cassette including a plurality of generally vertical compartments for storing sample tube racks and/or SBS formatted plates is constructed to be flexible along its substantially vertical axis thereby facilitating reliable robotic placement and retrieval of the cassette from nesting tubes located within a horizontal freezer compartment. Insulated walls and solid shelves minimize heat transfer from storage racks or plates placed in the storage cassette when the cassette is removed from an ultra-low temperature or cryogenic freezer. The outer walls of the cassette includes mechanical indexing locations to ensure appropriate positioning when robotically removing storage racks or plates from the cassette.