Can I use soap flakes to wash cloth nappies?

After all, that's how they washed nappies back in the olden days, before nappy sanitisers, right?

Soap flakes sound like a great option for cloth nappies - there are some lovely pure, all natural soaps that seem to fit really well with the environmental, chemical-free and money saving ideals behind cloth nappying. But it's not that simple. Most cloth nappy manufacturers actually recommend not using soap flakes to wash nappies (it can actually void your warranty) and there's science behind it.

Soap is such a great cleaner because it acts as a peacemaker between oil (like the fats in poo and other dirt) and water, and makes them get along. The soap keeps the oil particles suspended in the water so when you rinse the soap away, the oil (and all the dirt that is attracted to the oil) goes with it. All good!

So, why aren't soap flakes recommended for cloth nappies?

While soap is great, it's a bit of a fair-weather friend: it works well under ideal circumstances, but reacts REALLY easily to substances that may be in your washing load, causing it to either not work effectively, or actually create new issues. Here are a couple of the common problems affecting those of us who wash cloth nappies:

Problem 1

If soap is used in hard water (water that contains minerals like calcium or magnesium - bore water is typically hard, as is water in Brisbane and Adelaide), the soap reacts with the minerals to form insoluble salts - they make rings around your bath or scale in your shower or washing machine. It means nappies don't get cleaned thoroughly and it leaves an insoluble residue on fabrics, causing repelling, leaking and even irritation.

Here's the chemical reaction (for those who are interested in such things!):
2 CH3(CH2)16CO2-Na+ + Mg2+ becomes [CH3(CH2)16CO2-]2Mg2+ + 2 Na+

Problem 2
But even if you live in an area with softer water, soap flakes can still be problematic, as another chemical reaction can occur when soap is used in water that is acidic. Town water may not be too acidic (tankwater, however, generally is), but there is wide variation around the country - the Australian Drinking Water Guidelines are that the pH of drinking water should ideally be 6.5 to 8.5 (a pH of less than 7 is considered acidic). But there are also other acidic substances in our load of nappies - like urine (and lots of it!) - that can make the water more acidic. Additives like vinegar also increase the acidity.

Acidic water causes a reaction with soap that creates 'free fatty acids.' These fatty acids no longer dissolve in water, and cause a film or buildup on surfaces or - you guessed it - in nappies. And, as we know, any sort of build up - be it detergent/soap or ammonia - causes nappies to lose absorbency.

Here's the chemical reaction (once again, only for those who are interested!):

CH3(CH2)16CO2-Na+ + HCl becomes CH3(CH2)16CO2H + Na+ + Cl-

But soap was used for years for washing nappies, what's changed?

This is true, but they also used to boil the nappies - this helped dissolve and rinse out the soap and any residue and cut through oils, through sheer heat energy. And rinsing (and soaking) with bleaches was done too. Bleach increases the water solubility of fabric meaning water can penetrate the fibres, and it also interacts (another chemical reaction!) with any organic molecules to break them down through oxidation into smaller ones (that's why it can also damage fabrics).

But don't detergents work the same way as soap flakes?

Laundry detergents are specifically designed to overcome the issues that soap has - while many are soap-based, they are created to be soluble in both acidic and alkaline water, and don't react as badly in hard water (they can still react, which is why you generally need to use more detergent or higher water temperatures in hard water areas). They also tend to be better at lowering water's surface tension so it can penetrate the fabric fibres. Some detergents will perform better in your water with your washing machine than others - this is due to the different combinations of ingredients and how they interact with your laundry.

There are detergent options that are less harmful for the environment, reduce our children's exposure to chemicals and some that are specifically designed to clean cloth nappies effectively. You can find eco-friendly detergents in the supermarket that are suitable for nappies (as well as the rest of your washing), and we also have cloth nappy laundry detergents available.