Lung Volume Bags, Plastic Transparent

Quick Answer: A lung volume bag is a transparent plastic bag that collects exhaled air so that its volume can be measured. In physiology and biology practicals it is used to estimate vital capacity and tidal volume without a spirometer.

Measuring a Breath You Can See

Lung volumes stay abstract until students can see one. With a lung volume bag, a student takes the deepest possible breath and blows it all out through a mouthpiece into the empty bag, which swells to hold that single breath: the vital capacity. A quiet, relaxed breath out gives the much smaller tidal volume, and the contrast between the two makes the point of the practical in a way a textbook figure cannot.

The title describes the bags as transparent plastic. Whether the bags carry printed volume graduations is not stated. Where they do not, the collected air is measured by displacement: the bag is connected by tubing to an inverted, water-filled measuring vessel standing in a trough, and the bag is squeezed flat so the water pushed out equals the volume of the breath.

Results vary with body size, sex, age and fitness, so the practical works well as a class data exercise, for example plotting vital capacity against height or comparing students who play wind instruments or sport with those who do not. Treat the numbers as estimates: some air is lost at the mouthpiece and the method is not a clinical lung-function test.

Specifications

Applications

• Measuring vital capacity and tidal volume in school and college physiology practicals
• Class investigations linking vital capacity to height, sex or regular exercise
• Estimating expiratory reserve volume by blowing the air left after a normal breath out into the bag
• Pairing a real measurement with a bell-jar lung model that shows how the diaphragm moves air

Care & Handling

• Give every student a separate mouthpiece, and do not pass bags between students unless they are cleaned in line with the school’s hygiene procedure.
• Before each reading, roll the lung volume bag flat from the closed end to push out air left from the previous breath.
• Wipe the outside with a mild disinfectant, dry it, and store it flat away from sharp objects and heat, which split or distort thin plastic.
• Students with breathing difficulties should not be pushed into repeated forced breaths; they can act as recorders instead.

Why Choose LabEquip

Lung volume bags suit schools and colleges that want a hands-on breathing practical without buying a spirometer. LabEquip supplies them with related items such as the peak flow meter in its Biology Lab Products range.

Frequently Asked Questions

What is vital capacity?

The largest volume of air a person can breathe out after the deepest possible breath in. It is the sum of tidal volume, inspiratory reserve volume and expiratory reserve volume.

How do I read the volume if the bag has no scale?

Connect the bag by tubing to an inverted, water-filled measuring cylinder or bottle standing in a trough, then squeeze the bag flat. The volume of water displaced equals the volume of air that was in the bag.

Why does a bag reading differ from a spirometer reading?

Some air escapes around the mouthpiece and the bag may not be emptied completely, so bag readings are estimates. A spirometer measures the air directly and also records how fast it leaves the lungs.

Is it hygienic for a class to share the bags?

Only with a clean mouthpiece for each student and the bag cleaned in between. Many teachers issue one bag per group and one mouthpiece per student.

Can tidal volume be measured with the same bag?

Yes. The student breathes one normal, relaxed breath out into the empty bag. Averaging several breaths gives a steadier figure, because single quiet breaths vary.

Which factors should students compare in a vital capacity investigation?

Height, sex, age and regular aerobic training are the usual variables. Keep posture the same for every reading, because standing upright gives larger volumes than slouching in a chair.

Last Updated: September 2026