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Diaper “Wetness Indicators”

Posted by Baby by Jitta on

Have you ever wondered what those colour-changing strips found at the bottom of diapers are made of? Well, those are called “wetness indicators” and how they work is quite fascinating. Before we talk about the science behind this strip, we will need to take a look at what are they are used for and what causes the change of colour in the first place. Well, wetness indicators are used to show whether or not a baby has used his/her diapers. This gives an indication of when it’s time to change your baby’s diapers.

Baby Diapers

Now that we have an understanding of what the wetness indicator is used for, we should start talking about what causes the change in colour and the science behind this change. The change in colour is caused by the chemical “Bromophenol Blue” that is used to make these strips. When these strips are dry, their pH level tends to stay below 6 which means that it will be yellow. However, when wet, the pH level will rise to above 7.6 which will cause the Bromophenol Blue to turn blue.

There are tons more chemicals that react in similar ways when there is a change in pH levels. Some of these are the Universal Indicator, Thymol Blue, Phenol Red, Phenolphthalein, and Methyl Orange. However, almost every wetness indicator found in diapers uses Bromophenol Blue as it changes colour at a suitable pH range. Who knew that there were so much interesting things to learn about just by looking a little closer into diapers and the science behind these everyday objects.


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