Technical Foundation
What Is a Bottle Cap?
Bottle caps are specified by thread finish first — GL threads (GL18, GL25, GL45, etc.) are the standard for laboratory glassware and screw directly onto matching GL-finish bottle necks, while continuous thread (CT) finishes like 28-400 or 38-400 are the standard for commercial packaging bottles, with the two numbers denoting neck diameter in millimeters and thread series respectively.
Liner and seal material must match the bottle's contents chemically: PTFE liners resist solvents and aggressive chemicals that would degrade a standard foam or PE liner, while an induction heat seal adds tamper evidence and an extra vapor barrier for liquids sensitive to oxidation or moisture ingress during storage and shipping.
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| Spec | What It Means | Why It Matters |
|---|---|---|
| Thread Finish | GL (GL18/25/32/45) vs. continuous thread (20-400, 28-400, 38-400) | GL is the lab-glassware standard; CT is the commercial packaging standard — not interchangeable |
| Liner Material | PTFE, foam (PE/EVA), induction seal foil | PTFE resists solvents and aggressive chemicals that degrade standard foam liners |
| Cap Material | Polypropylene, HDPE, phenolic | Chemical compatibility with contents and closure torque strength vary by resin |
| Closure Type | Screw cap, dropper cap, child-resistant, flip-top | Function and end-user access requirements drive closure mechanism selection |
| Seal Type | Induction heat seal, tamper-evident band | Adds vapor barrier and visible evidence of prior opening for regulated or sensitive contents |
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Applications
Where Bottle Caps Get Used
Bottle caps are specified anywhere a threaded closure must match a specific bottle neck finish while providing the right chemical resistance and tamper evidence for the contents.
Laboratory & Analytical Chemistry
GL45 PTFE-lined caps on solvent storage and reagent bottles resisting chemical attack on the liner.
Pharmaceutical & Nutraceutical Packaging
Child-resistant continuous-thread caps with induction seals meeting regulatory tamper-evidence requirements.
Industrial Chemical Packaging
Chemical-resistant screw caps on drums and jugs holding solvents, acids and cleaning concentrates.
Cosmetics & Personal Care
Dispensing and dropper caps on packaging requiring controlled, metered product delivery.
Food & Beverage Bottling
Tamper-evident continuous-thread caps providing consumer assurance of an unopened seal.
Water Treatment & Sampling
GL-thread caps on sample bottles used in field and lab water quality testing.
FAQ
Bottle Caps Questions, Answered
What's the difference between GL thread and continuous thread (CT) bottle caps?
GL thread finishes (GL18, GL25, GL45, etc.) are the international standard for laboratory glassware and specify both diameter and thread pitch precisely. Continuous thread (CT) finishes like 28-400 or 38-400 are the standard for commercial packaging bottles — the two numbers denote neck outer diameter in millimeters and a thread-series code. The two systems are not interchangeable.
When do I need a PTFE-lined cap instead of a standard foam liner?
PTFE liners are needed whenever the bottle contents are solvents, strong acids/bases, or other aggressive chemicals that would swell, dissolve or otherwise degrade a standard polyethylene foam liner over time, causing leaks or contamination.
How do I know what thread finish my existing bottles use?
Measure the outer diameter of the bottle neck and count threads, or check the bottle manufacturer's spec sheet — for lab glassware this is usually stamped as a GL number; for packaging bottles it's typically printed as a diameter-series code like 38-400 on the supplier's data sheet.
What is an induction seal and when is it required?
An induction heat seal is a foil liner bonded to the bottle neck by an induction sealing machine after filling, creating a hermetic seal that's broken visibly on first opening. It's commonly required for pharmaceuticals, nutraceuticals and some food products to demonstrate the product hasn't been tampered with or previously opened.
Can I use a child-resistant cap on any bottle?
Only if the cap's thread finish matches the bottle neck exactly — child-resistant mechanisms (push-and-turn, squeeze-and-turn) are built onto specific thread finishes, so it must be ordered to match your existing bottle's neck finish, not selected independently.
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