Protecting microbiology samples and tissue cultures from bacteria, the cellulose stoppers snugly fit in test tubes or Erlenmeyer flasks. Routinely used in laboratories, the breathable closures permit with air flow for when a complete tight seal is not necessary. Due to the organic compound manufacturing and hydrophilic physical properties, closures are for single use only. The standard, thick, or specialized shaped cellulose stoppers come in different diameters to fit any opening needed.