8 mm Test Tube Stoppers — LDPE, Natural, Plug-In Friction Fit (300-2908-020), 1000/Bag
These natural Low-Density Polyethylene (LDPE) stopper caps are designed to close 8 mm OD test tubes with a plug-in friction fit, seating against the inner tube wall to prevent evaporation, contamination, and spillage without any threading or snap-over engagement. Supplied non-sterile in bulk packs of 1000, they are the standard choice for high-throughput tube-capping programs across clinical, research, and microbiology workflows. LDPE's inherent flexibility allows the stopper plug to compress on insertion and recover to maintain a retained seal across a temperature range of −20°C to +60°C, including freeze-thaw cycling.
Technical Specifications
| Specification | Value |
|---|---|
| Part Number (MPN) | 300-2908-020 |
| Tube OD | 8 mm |
| Cap Style | Stopper — plug-in friction fit |
| Material | Low-Density Polyethylene (LDPE) |
| Color | Natural |
| Temperature Range | −20°C to +60°C |
| Sterility | Non-Sterile |
| Pack Size | 1000/Bag |
| BPA / Phthalates | BPA-free; no phthalate plasticizers |
| Country of Origin | USA |
Applications
- Microbiology culture tube capping — seals TSB, BHI broth, and similar culture tubes during incubation to prevent contamination while permitting gas exchange characteristic of friction-fit stoppers
- Specimen tube archiving — closes serum, plasma, and urine tubes during refrigerated and frozen storage, maintaining a friction-retained seal through repeat freeze-thaw cycles
- Clinical chemistry pre-analytical hold — prevents evaporation from sample tubes during batched processing or instrument queue time
- Research reagent storage — caps buffer, stock solution, and reagent tubes where a low-cost, resealable closure is preferred over screw caps
- Pneumatic tube transport — friction-fit retention reduces the risk of stopper dislodgement during transport through tube systems
Chemical Resistance
| Reagent / Condition | Compatibility |
|---|---|
| Aqueous buffers / saline | Excellent |
| Urine, serum, plasma specimen matrices | Excellent |
| Broth culture media (TSB, BHI) | Excellent |
| Dilute acids and bases | Good — short-term contact |
| Ethanol (<70%) | Good — short-term contact |
| Aromatic or chlorinated solvents | Not recommended |
| Freeze-thaw cycling (−20°C) | Excellent — LDPE retains flexibility at low temperature |
Quality & Procurement
Made in USA, these Caplugs® Evergreen stopper caps are manufactured from BPA-free, phthalate-free LDPE resin. The LDPE flex modulus is the essential material property for stopper-format closures: it allows the plug to compress under insertion force and recover against the inner tube wall without fracturing — the failure mode that makes rigid polymers such as PP or PS unsuitable for this cap style. LabSupplies.com is an authorized Caplugs® Evergreen dealer and ships from USA inventory, with tiered pricing available for clinical labs, hospitals, research institutions, and biotech facilities operating high-volume tube-capping programs.
Frequently Asked Questions
Why must these stoppers be LDPE rather than polypropylene or polystyrene?
The stopper-plug design relies on the cap compressing slightly under insertion force and then recovering to press against the inner tube wall by friction. LDPE's low flex modulus provides exactly that behavior. Rigid polymers such as PP and PS lack sufficient give and would crack or fail to seat reliably, particularly at cold storage temperatures.
Will these stoppers hold up through freeze-thaw cycling?
Yes. LDPE maintains its flexibility from −20°C frozen archive conditions up to +60°C incubation temperatures, so the friction-fit engagement is preserved through repeat freeze-thaw cycles without the stopper hardening or loosening.
Are these stoppers sterile?
No — the 300-2908-020 is supplied non-sterile in 1000/Bag bulk packaging. For workflows requiring sterile closures, contact our sales team to discuss available options within the Caplugs® Evergreen product line.
What tube types are compatible with this stopper?
These caps are sized for 8 mm OD test tubes, including small-format disposable glass and polystyrene culture tubes commonly used in microbiology and clinical chemistry. If your tubes have a different outer diameter, Caplugs® Evergreen offers stopper caps in 9 mm and 10 mm OD sizes as well.