Test Tube Stoppers, Thin-Wall, HDPE, Natural — 300-2908-020 | 1000/Bag | Caplugs® Evergreen

Test Tube Stopper Caps for 8 mm Test Tubes, LDPE, Natural — 300-2908-020 | 1000/Bag

Technical Narrative

The Caplugs® Evergreen is a natural Low-Density Polyethylene (LDPE) stopper cap for 8 mm OD test tubes — a plug-in friction-fit closure designed for small-format test tubes, micro test tubes, and culture tubes in the 8 mm OD range. The stopper plug inserts into the tube opening and seats against the inner tube wall by friction, providing a positive retained closure that prevents evaporation, contamination, and spillage during culture incubation, specimen archiving, refrigerated storage, and pneumatic tube transport without threading or snap-over engagement. Natural LDPE stoppers are the universal default, compatible with all standard labeling methods and suitable for any workflow where a secondary barcode or written identification system is the primary specimen identifier.

LDPE is the required material for stopper-style tube caps because its low-density polyethylene flex modulus allows the stopper plug to compress under insertion force and recover to retain against the tube inner wall without fracturing — the failure mode that makes rigid materials (PS, PP, HDPE) unsuitable for stopper-format closures. LDPE maintains this flexibility across the full storage temperature range from -20°C frozen archive to +60°C incubation, ensuring stopper retention through freeze-thaw cycles without hardening or losing friction-fit engagement at low temperatures. LDPE chemical inertness to aqueous specimen matrices (urine, serum, plasma, broth media) ensures no cap leaching into tube contents during storage.

At $45.45 per 1000/Bag — $0.0455 per stopper — the delivers 8 mm natural LDPE tube closure at per-stopper economics for high-volume tube capping programs. Available across the full Caplugs® Evergreen stopper range: 300-2908-G20 (Green 8 mm, $45.45/1000); 300-2909-020 (Natural 9 mm, $46.60/1000); 300-2910-020 (Natural 10 mm, $44.43/1000).

Technical Specifications — Caplugs® Evergreen

Test Tube Stopper Application Compatibility —

The 8 mm natural LDPE stopper cap fits small-format test tubes, micro test tubes, and culture tubes in the 8 mm OD range for the following workflows:

Always validate stopper fit with your specific tube brand and lot before bulk purchase — tube opening diameter can vary slightly between manufacturers within the 8 mm OD range. Request a free sample to confirm friction-fit retention before committing to volume.

Chemical Resistance — Low-Density Polyethylene (LDPE)

LDPE provides the flexibility essential for stopper-style tube caps — it compresses and springs back under insertion and removal forces without fracturing, while resisting the aqueous specimen matrices it contacts in clinical and laboratory tube workflows.

Laboratory Applications

The serves clinical and research microbiology laboratories capping culture tubes during incubation; clinical chemistry and hematology labs archiving specimen tubes in refrigerated and frozen storage; research labs capping reagent and buffer stock tubes between uses; cell culture programs capping suspension culture tubes during incubation; environmental and field sampling programs capping sample collection tubes; and any laboratory workflow requiring friction-fit sealed closure on 8 mm OD test tubes.

U.S. Manufacturing, Quality & Institutional Procurement

Every Caplugs® Evergreen lot is precision-molded at our California manufacturing facility and subject to rigorous dimensional inspection and material purity verification. We supply reference laboratories, hospital systems, and federal procurement offices under institutional pricing programs with blanket-order support and same-day shipping on stocked inventory. Request a free sample below to validate stopper fit with your specific tube brand before committing to volume.

Frequently Asked Questions — Caplugs® Evergreen

What test tube OD does the stopper fit?

The is designed for test tubes with a 8 mm outer diameter (OD) — the tube's outer dimension. This includes Disposable glass/PS culture tubes, small-diameter polystyrene test tubes, hematocrit tubes with stopper caps, and thin-wall tubes in micro-analytical formats. Always validate stopper-to-tube fit with a sample before bulk purchase — tube opening diameter can vary slightly between manufacturers and within the 8 mm OD range depending on wall thickness. Request a free sample to confirm friction-fit retention before committing to volume.

Why is LDPE specified for test tube stopper caps rather than PP or PS?

Stopper-style tube caps work by friction fit — the plug compresses under insertion and recovers against the inner tube wall. This requires a material with sufficient flex modulus to compress and spring back without fracturing. PP and PS are too rigid — they would crack under the repeated insertion/removal forces of high-volume tube workflows. LDPE's low-density flex allows repeated stopper insertion and removal across thousands of cycles without fracture, while retaining enough spring-back to maintain friction-fit seal retention against the tube wall. LDPE also retains flexibility at -20°C, preventing brittle fracture during frozen archive stopper removal.

What is the difference between Natural and Green LDPE stoppers for 8 mm tubes?

Natural LDPE stoppers and Green LDPE stoppers (300-2908-G20) are identical in material and performance — both fit 8 mm OD tubes with the same friction-fit retention. The only difference is color. Natural is the general-purpose default for any workflow using secondary barcode or label identification. Green enables color-coded specimen-type or batch routing in laboratories where visual differentiation of stopper color in racks is a workflow efficiency requirement.