Plastic lab test tubes are the clear or translucent tubes you see in clinics, classrooms, kitchens, and home test kits. They hold small amounts of liquid or powder, and they come in many sizes with many kinds of tops. Knowing how they are measured and what each style is for makes it much easier to choose the right one. This guide covers the plastics used, the standard sizes, the types of tops, and the most common uses.
What Are Plastic Lab Test Tubes?
A test tube is a narrow, finger-length container with a rounded or tapered bottom and an open top. Glass versions have been used for centuries, but plastic versions have become very common because they are lightweight, shatter-resistant, and inexpensive enough to be used once and thrown away.
They are sold in two main forms: sterile (ready for samples that must stay clean) and non-sterile (fine for general mixing and storage). Most are packed in bulk bags or in racks that hold them upright.
Common Plastics and What They Mean for You
The plastic type affects clarity, temperature tolerance, and chemical resistance. Look for a small resin code or material note on the packaging.
- Polypropylene (PP): Slightly cloudy but tough. Resists many chemicals, handles freezing and boiling water, and can often be steam-sterilized in an autoclave. This is the most common choice for general lab work and for tubes that will be spun in a centrifuge.
- Polystyrene (PS): Crystal clear, so contents are easy to see. It is not heat resistant and can crack when exposed to solvents, so it suits single-use culture work and everyday viewing tasks rather than hot liquids.
- Polycarbonate (PC): Very strong and clear, with high impact resistance. It costs more and reacts with some chemicals, so it is chosen when durability matters most.
- PETG: Clear with good gas barrier properties. Often used for diagnostic and specimen tubes.
- Polyethylene (PE): Flexible and low cost. Used for simple, low-demand tasks.
A quick rule: match the tube to the temperature and the liquid it will hold. When in doubt, choose polypropylene.
Sizes: How Test Tubes Are Measured
Test tubes are usually described by two numbers: the outside diameter and the length, both in millimeters. The capacity is given in milliliters (mL). For example, a 12 x 75 mm tube is about 12 mm wide and 75 mm long and holds roughly 5 mL when filled to the very top.
The table below shows the most common sizes and what they are typically used for.
| Nominal size | Approximate capacity | Typical use |
|---|---|---|
| 10 x 75 mm | 3 mL | Small samples, classroom work, crafts |
| 12 x 75 mm | 5 mL | General sample collection and testing |
| 13 x 100 mm | 6–7 mL | Routine lab procedures |
| 16 x 100 mm | 10 mL | Mixing, diluting, small reactions |
| 16 x 125 mm | 15 mL | Storage and culture work |
| 16 x 150 mm | 18–20 mL | Larger culture and sample volumes |
| 25 x 150 mm | 45–50 mL | Bulk samples and demonstrations |
Bottom shape matters too. Round-bottom tubes are the classic shape and are easy to swirl. Conical-bottom tubes (sometimes called centrifuge tubes) collect solid material in a small point at the base, which makes them useful for separating liquids from solids. Some tubes have a flat or skirted base so they can stand on their own without a rack.
Rimmed vs. rimless: A rimmed tube has a small lip at the top, which lets a stopper or cap grip better. Rimless tubes have a smooth edge and are usually sealed with a screw cap that threads over the outside.
One important point: the listed capacity is the tube filled to the brim. In real use you fill only partway, so the working volume is lower. That headspace allows for mixing and prevents spills.
Tops and Closures
The top you choose controls how well the tube seals, how easy it is to open, and whether air can get in.
Screw caps
Threaded caps twist on and off and provide the best seal, especially when fitted with an inner liner or O-ring. They are the standard choice for storage, transport, and any tube that will be spun or shaken.
Snap caps
These push on with light pressure and pop off quickly. They are convenient for high-throughput work but are not fully leakproof, so they are not ideal for liquids that may tip over.
Plug or push-in caps
Low-cost caps that fit loosely into the tube opening. They keep dust out while still allowing some air exchange, which is useful for certain cultures but not for long-term sealing.
Vented or dual-position caps
These can be tightened for a seal or left partly open to allow gas exchange. They are common in microbiology, where organisms may need airflow.
Stoppers
Rubber or silicone stoppers press into rimmed tubes. They seal well but are harder to handle in bulk and are usually reserved for temporary closures.
What Plastic Test Tubes Are Used For
Their simple shape makes them useful in many settings:
- Sample collection and transport: urine, swabs, water, and other specimens.
- Diagnostic testing: holding reagents and samples in test kits and clinics.
- Centrifugation: spinning samples to separate liquids, cells, or solids.
- Storage and freezing: keeping small amounts of samples or chemicals.
- Culture work: growing microorganisms in a controlled container.
- Mixing and diluting: combining small volumes of liquid or powder.
- Water, soil, and pool testing: checking pH, chlorine, and other readings.
- Education: classroom experiments and science demonstrations.
- Household and hobby use: storing beads, spices, seeds, or small craft items.
Plastic vs. Glass Test Tubes
Plastic wins on safety and convenience. It does not shatter, it weighs less, and single-use versions reduce the risk of cross-contamination. Glass wins on clarity, heat resistance, and resistance to harsh chemicals, and it can be washed and reused many times.
As a simple guide: choose plastic for transport, one-time use, and safety around breakage. Choose glass when you need to heat the tube directly or work with aggressive solvents.
How to Choose the Right Tube
- Start with the volume. Estimate how much liquid you need, then add room for headspace.
- Pick the bottom style. Round for mixing and viewing, conical for separating solids, skirted for standing upright.
- Decide on the cap. Screw caps for sealing and transport, snap or plug caps for quick access.
- Check the plastic type. Confirm it suits your sample, temperature, and any chemicals involved.
- Confirm sterility needs. Choose sterile tubes for clinical or culture work.
- Check the fit. Make sure the tube matches your rack, centrifuge, or testing device.
Handling, Cleaning, and Disposal Tips
- Do not overfill. Leave space so the liquid can move without spilling.
- Label tubes on the side with a marker or tape. Avoid covering the whole tube so you can still see the contents.
- Balance tubes in a centrifuge and stay within the fill limits given by the manufacturer.
- Never heat a plastic tube over an open flame. Use a warm water bath instead.
- Most plastic tubes are designed for one use. If you reuse one, rinse it well, let it air dry, and make sure the plastic is compatible with what you will put in it.
- Dispose of tubes that held biological samples as biohazard waste, following local rules.
Quick Answers to Common Questions
Are plastic test tubes reusable?
Some are, but many are intended for a single use. Polypropylene tubes hold up best to washing and reuse.
Can plastic test tubes be autoclaved?
Polypropylene usually can. Polystyrene and some other plastics will warp or melt, so always check before heating.
Do all caps fit all tubes?
No. Caps are matched to a specific diameter and thread pattern. A cap from one size will rarely seal another.
What does working volume mean?
It is the amount you can safely put in the tube during normal use, which is less than the full capacity.
The Bottom Line
Plastic lab test tubes are simple tools with a surprising amount of variety. The plastic type sets the temperature and chemical limits, the size sets the volume, and the bottom shape and cap decide how the tube is handled. Match those three things to your task, and you will have the right tube for the job every time.
If you found this helpful, explore more practical guides on everyday tools, storage, and household testing so you can keep getting quick, reliable answers.