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How Does the Wetness Indicator Change Color? It's Not Magic – It's pH.
It's Not Magic – It's pH
The wetness indicator adhesive contains a pH sensitive substance. Healthy baby urine is usually slightly acidic to slightly alkaline. When urine soaks through the diaper core and reaches the indicator strip, the pH changes, and the colour changes accordingly. It's the same process as using pH paper to test a solution – different pH levels produce different colours.
The most common colour change for mainstream wetness indicators is from yellow to blue. Faster response products give a vivid, clear colour change that is easy to see.
Two Types of Wetness Indicator Technology
There are two types of wetness indicator technology used in baby diapers:
One is the hot melt type (colour change type) , which works by pH change – this is the mainstream technology today.
The other is the ink type (fade out type) , which works on a simpler principle: the coloured pigment is washed away by urine, leaving no colour. This is a physical change, not a chemical reaction. However, the colour change type is more intuitive – you see the colour change and know it's time to change the diaper, rather than having to notice "the colour is gone."
⭐How Is the Wetness Indicator Adhesive Made?
The wetness indicator adhesive is essentially a special hot melt adhesive. Besides the base resin (such as SBS or SIS elastomers), tackifying resin, softeners, and antioxidants, its formulation includes a pH indicator – the key ingredient that causes the colour change. The pH indicator is typically added at 0.1% to 1%. Some products also include surfactants to help the indicator wet faster when in contact with urine, speeding up the colour change.
What Buyers Care About Most: Is It Safe?
The wetness indicator adhesive is applied on the inner side of the backsheet – the side facing the core – so it is separated from the baby's skin by the absorbent core. Reputable manufacturers use wetness indicator adhesives that have passed safety tests – they are non toxic and reliable. As for rumours about "Europe banning wetness indicators", there is currently no credible evidence – several diapers with the Nordic Swan Ecolabel still feature wetness indicator strips.