Centrifuge Tube, Round Bottom, Plastic

Quick Answer: The Centrifuge Tube, Round Bottom, Plastic is a plastic centrifuge tube with a hemispherical base instead of a pointed cone. A round bottom centrifuge tube spreads spun material over its curved base, mixes and resuspends easily, and is used for small bacterial cultures, cell washing and general spins where a vortex mixer is part of the method.

What the Rounded Base Changes

A rounded base has no sharp point where stress concentrates, which is one reason tubes intended for higher centrifugal forces are commonly made with round bottoms. The curve also lets liquid swirl freely: a vortex mixer or a flick of the finger resuspends a pellet quickly, and a loosely capped tube of this shape in a shaking incubator gives a broth culture good aeration.

The trade-off is the pellet. Instead of gathering at a point, spun material forms a thinner layer over the curved bottom, so decanting must be slower and very small pellets can be hard to see. For routine pelleting where the pellet must be visible and the supernatant poured off cleanly, the conical bottom tube fits better; where mixing, culturing or resuspension matter more, round bottom tubes are preferred.

Plastic round bottom tubes are made in polypropylene, which resists most aqueous reagents and can generally be autoclaved, and in polystyrene, which is clearer but not autoclavable and is the usual material for flow cytometry sample tubes. The plastic, volume and cap type of this listing are not given in the title, so match them to your rotor and method before ordering.

Specifications

Care & Handling

• Keep round bottom tubes in a rack or tube box, as they cannot stand unsupported
• Pour off supernatant slowly, with the tube tilted away from the pellet side
• Use rotor adaptors that support the rounded base fully, so the tube is not strained at the rim
• Discard tubes that show cracks, cloudiness or distortion after autoclaving

Applications

• Growing small bacterial broth cultures overnight in a shaking incubator
• Washing cells by repeated spinning and resuspension on a vortex mixer
• Preparing cell suspensions for counting or flow cytometry
• General separation of precipitates and suspensions in biochemistry practicals

Why Choose LabEquip

Microbiology and immunology teaching labs, research groups running cell washes and flow cytometry, and labs growing many small cultures are the main buyers of round bottom tubes. LabEquip stocks them beside conical and self-standing tubes in the Biology Lab Products range; send volume and rotor details via our contact page.

Frequently Asked Questions

When should I choose a round bottom tube over a conical one?

Choose round bottom tubes when samples need frequent mixing or resuspension, for small broth cultures, or when the method calls for a rounded base. Conical tubes are better when a compact, visible pellet matters most.

Are round bottom tubes stronger in a centrifuge?

A rounded base spreads stress evenly and avoids the weak point of a cone, which is why many high-speed tube designs are round-bottomed. The real limit, though, is the tube’s own speed rating, which must not be exceeded.

Why are round bottom tubes used for bacterial cultures?

The curved base lets broth swirl and take in air as the tube is shaken, and cells resuspend easily before sampling. A loosely fitted cap keeps air exchange going during overnight growth.

Can polystyrene round bottom tubes be autoclaved?

No. Polystyrene softens and deforms well below autoclave temperatures, so these tubes are normally supplied sterile and used once. Polypropylene tubes are the ones that can generally be autoclaved.

How do I avoid losing a thin pellet?

Mark the outer side of the tube before spinning so you know where the pellet will lie, then decant or pipette slowly from the opposite side. A short, gentle respin collects any liquid that has run back down.

Do round bottom tubes need special rotor adaptors?

They need adaptors or buckets that match the tube diameter and support the curved base. Adaptors shaped for conical tubes can leave a round base unsupported, which stresses the tube during the spin.

Last Updated: September 2026