The Temperature Question

What is the best temperature to wash cloth nappies at?

This question is really made up to two questions: a) how washing temperature affects bacterial presence on nappies b) how washing temperature affects the life of a nappy.

Updates to the protocol are in green. These are changes we made as we went along, which happened when experimenters had questions we hadn’t thought about in the planning stage.

To test the first:

1. Each volunteer will have to first run their machine empty on a 90ºC wash, to eliminate the risk of contamination from the machine. Then each person will test a regular load of nappies at each of the following temperature: 30ºC, 40ºC, and 60ºC (making sure to do a 90ºC rinse before each load), using a standardized detergent used in industry testing. 30 experiment packs were sent out for this experiment, however due to dropouts only 18 were returned.
2. Each volunteer will then swab one nappy from each temperature wash and s guide on how to swab will be provided. A set date will be given for the volunteers to conduct their tests, so that all the swabs can be returned to the lab at the same time. For example, the 30ºC test will take place one week, then followed by the 40ºC the next. The samples should be posted first class back to the labs, because each sample needs to be sent immediately. Each volunteer will also fill out a survey with the following information: child age, location, water hardness, washing machine type, washing machine age, nappy material washed, approximate age of nappies and drying method used.
3. In the lab, colonies of bacteria will be extracted and the strains purified so that a lab grade bacterial sample is achieved. Swatches of the following fabric: cotton, microfibre, bamboo, fleece, pul; will be inoculated with the strains. These will then be washed at 30ºC, 40ºC, 60ºC, and 90ºC in a domestic machine and tested for bacterial presence.
3. Bacterial growth on agar plates for each temperature group will finally be compared.

To test the second:

1. Each volunteer will record which washing machine they have, the age of the machine, what rinse speed they use, whether it is an Eco Saver machine and what is their water hardness.
2. Volunteers will then be split into teams, each one testing the effect that multiple washes at either 30ºC, 40ºC or 60ºC have on nappies. Teams will be split so to have a mix of machine types and water hardness, to account for possible effects these might have on the nappies.
3. Four new and identical mixed sets of nappies will be purchased for the experiment, one control and one each to be used by each temperature team.
4. Each set of nappy will be sent to one volunteer from each team, who will run 20 washes with it at either 30ºC, 40ºC or 60ºC, depending on the team. Nappies will not be required to dry between washes. The nappy velcro is to be stuck down so that it does not damage the nappies
5. After 20 washes, the nappy will be sent to another volunteer from the same team, who will run another 20 washes at the same temperature.
6. After the nappy has been washed by all 5 members of the team, it will have gone through 100 washes at the same temperature. Nappies will then be inspected for balding, visual condition (staining or discolouration) and smell, as well as for elasticity (measuring the un-stretched elastics) and dimensional change. They will also be checked for absorbency, by measuring what volume of water each absorbs. It was intended that each volunteer tested the nappies after they had completed their 20 washes. However in practice the instructions for the absorbency and elasticity experiments were not clear so not everybody measured the same thing, and balding was not the only damage the nappies experienced. These experiments were repeated at the end.

We have chosen to use domestic machines rather than laboratory machines or laundrettes because, whilst being aware that domestic machines don’t always reach full temperature, we want to recreate a real life scenario as much as possible. By mixing machine types in each group, we aim to account for the possible small differences in temperature that each machine may reach.

There will also be desk-based industry research: members of the NSG Temperature working group will send a standardised email to a wide selection of nappy manufacturers, including international, national and local (e.g. home-based) companies, asking questions around their washing guidelines and how these are set. Where these are entirely based on fabric supplier guidelines this will be pursued where possible. This answers will be compiled and then examined and summarised to assess (i) methods manufacturers use to set their washing guidelines (ii) how this varies e.g. by company location and size (iii) whether recommendations are usually based on lab tests (iv) how consistent guidelines are in terms of wash temperature (controlled for fabric type) (v) whether a particular wash temperature is dominant in the recommendations.