If your product is available in multiple sizes, it is natural to ask: do I need to test every size?
The answer is not always straightforward. In many cases, not every size will need to be tested, but that depends on several important factors that need to be considered carefully.
Start with the product standard
The first and most important point is always the product standard itself. Some standards clearly state which size, or how many sizes, must be tested. In some cases, the requirement may be to test specific sizes. In others, it may be necessary to test all sizes. For example, in EN 140, certain clauses include wording such as: “Two samples of each size shall be tested.” Where a standard gives clear direction, those requirements must be followed as a minimum.
Consider the worst-case scenario
Where there is some flexibility, the next step is to identify what would represent a worst-case scenario. This means determining which size is most likely to present the greatest challenge in terms of performance. Depending on the product design, that could be:
- The smallest size, where fit and resistance may be more demanding,
- The largest size, where increased internal volume could influence results or;
- A size with specific design features that make it particularly important to assess.
By testing a worst-case sample, it may sometimes be possible to demonstrate compliance across a range of sizes without needing to test every individual variant.
Human subject testing may require multiple sizes
The approach can change when testing involves human subjects, such as during practical performance or inward leakage testing. In these cases, it is important that the product size is matched to the wearer using the manufacturer’s sizing information. This ensures the testing reflects realistic conditions of use. As a result, multiple sizes may be required, so that each test subject is wearing a product that fits appropriately.
Size can directly affect performance
While the aim is always to optimise testing programmes and avoid unnecessary duplication, it is important to recognise that, for some tests, size can have a direct impact on performance. A good example is CO₂ content of the inhalation air, where differences in internal volume between sizes can directly influence the result.
The right approach depends on several factors
Ultimately, the number of sizes that need to be tested will depend on:
- The requirements of the relevant standard,
- The design differences between sizes and;
- The type of testing being carried out.