A flexible and porous material designed to securely hold a biopsy specimen within a tissue cassette, to prevent loss of the specimen during specimen processing (e.g., fixation, dehydration, infiltration) in preparation for subsequent cytological or histological examination. The flexible and porous material (e.g., paper, synthetic polymer) is intended to allow infiltration of reagents and maximize fluid-exchange during tissue processing. It is available in various forms (e.g., sheet, bag, foam pad) and is placed in a tissue processing cassette, with the biopsy specimen wrapped or contained inside it. This is a single-use device.