(With thanks to Elmarie Robson from Mini Matters for the information provided below)
Modern cloth nappies are made of various types of fabrics. The outer is normally a waterproof or water repellent fabric and the inside has the fabric that absorbs.
Waterproof vs Water repellent
The two types of waterproof fabrics used in modern cloth nappies are PUL and Waterproof Softshell. The part that makes them waterproof is the same – a breathable polyurethane (PU) film.
PUL (Polyurethane Laminate Fabric) - waterproof
These fabrics consist of a breathable polyurethane (PU) film that is permanently bonded to a base fabric (usually polyester when used in cloth nappies).
There are 2 ways that PUL fabric is manufactured:
Chemical bonding – this method uses a chemical process to attach the PU film to the base fabric. This method is considered old fashioned because it is not environmentally friendly. It is still used in the medical industry as it can withstand the high temperatures needed for autoclaving.
Thermal bonding – also known as TPU, uses a hot melt process to create a permanent bond. This is what most cloth nappy retailers would use in their PUL nappies. It’s pliable and soft so works very well for cloth nappies. It’s also environmentally friendly as the production process does not emit any toxic waste or VOCs (volatile organic compounds).
Waterproof Softshell Fabric
This is a type of PUL fabric. The waterproof PU layer is sandwiched between two layers of fabric, so it is not exposed. Usually, it would be 100% polyester + polyurethane + microfleece. So, it’s a 3-layer fabric instead of 2-layers like regular PUL. This makes it thicker and slightly less breathable than regular PUL, however some prefer it for the soft, fleecy inner layer.
Benefits to using cloth nappies with a waterproof PU layer are:
It’s soft and breathable, a very comfortable fabric.
Regular 2-layer PUL is thin and trim.
It offers very good waterproof protection.
Durable and long lasting provided it is not repeatedly exposed to high temperatures or direct sun.
Potential drawbacks to using nappies with a waterproof PU layer are:
It is synthetic (man made) and some babies may have a sensitivity to synthetic materials.
Not as breathable as other all natural fiber alternatives like wool and fleece (but more breathable than disposable nappies).
It may deteriorate more easily if not well looked after.
The three types of water repellent/resistant fabrics are Polyester Fleece, Water Resistant Softshell and Lanolised Wool
Polyester Fleece (Water resistant)
Microfleece lets moisture through and is good for a stay-dry lining inside a pocket nappy or for re-usable liners. Polar fleece repels water and is good for use as a water repellent nappy cover.
Lanolised Wool (Water resistant)
Wool covers (soakers) can be used as covers for overnight use too. One needs to lanolise them using lanolin (sheep wool fat). Wool soakers are normally knitted or crocheted using 100% pure merino wool. No buts. 100% pure merino wool. Sheep’s wool, which will make high quality soakers.
Water Resistant Softshell fleece
Works in a similar way to polar fleece by repelling water. This type of softshell fabric does not have a waterproof layer inside and usually consists of two layers; 100% polyester + microfleece that are bonded together.
Water repellent/resistant fabrics are great for overnight use for babies who tend to need a little bit more breathability for overnight use
One of the aspects that sets nappy types apart are the layers used for absorbancy. Options are synthetic fabrics and/or natural fibres. An example of a synthetic fabric is microfibre (polyester). Natural fibre examples are cotton, hemp, bamboo or a mixture of them.
Microfibre needs pressure to absorb and it absorbs fast. A con is that it could lead to compression leaks. Microfibre inserts are similar to sponges. You press a wet sponge, the liquids will run out. Keep in mind that Microfibre can never go directly against baby's skin (it absorbs too fast and could dry out your baby's skin). Always use them inside a pocket or cover it with a liner to protect baby's skin. Microfibre inserts dry quickly. The pocket lining (microsuede (polyester)) of pocket nappies are also a synthetic fabric but has a stay dry feel for baby.
Natural fibres contain liquids well and are trim options for inserts. Natural fibres can go against baby's skin. Note that baby can feel wetness with natural fibres (it doesn't have a stay-dry feel). For most babies this is not a problem at all, natural fibres can feel a lot more comfortable than synthetic fibres. Natural fibres are recommended for overnight use because it contains liquids better than microfibre. Natural fibres tend to become hard when dried in the sun. A quick rub between your hands will soften them. You could also throw them into your tumble drier for ten minutes to soften them.
Cotton is a natural fibre that stays soft. It is easily available and one of the most affordable options when it comes to natural fibres. Its durability is also an advantage since it’s not particularly sensitive to different PH levels in the case of a baby with acidic urine.
Bamboo is a natural fibre that is very trim. It is considered a relatively delicate fabric and is often blended with cotton or polyester to help strengthen it. Bamboo fabric comes in varying qualities and weights. The advantage of bamboo fabric is its ability to absorb very fast and its softness (this can vary depending on the quality and blend).
Hemp has an excellent trimness vs absorbent ratio, so it can hold a lot of moisture for it's trimness, hence being especially popular for night time cloth. Hemp do tend to get stiff when line dried therefore requires you to rub or tumble dry them to soften up. Hemp absorbs slower than other fabrics. That’s why some pocket nappies have 1 microfibre and 1 hemp insert. A great combination – microfibre that absorbs fast, paired with hemp that absorbs slowly but contains liquids well. So the hemp inserts catches the “overflow” from the microfibre insert. Hemp/cotton blend inserts work excellent for this reason as well, the cotton will absorb quickly and the hemp will hold on to the moisture
It is overwhelming to choose which types of fabric to use. At first, you will need to establish whether your little one is sensitive to any of the fabrics used (This is rare). Keep in mind though that some babies might develop a sensitivity at a later stage, a previous sensitivity can also disappear as baby gets older. They like to keep us on our toes, don’t they? Sensitivities are easily and cheaply handled by using liners (stay-dry if baby reacts to wetness or cotton if baby reacts to synthetic fabrics in a cloth nappy).
The above fabrics are a guideline for the qualities you would generally find in fabric stores, however the absorbency is not always determined by the type of fabric but rather its weight. Weight of fabric is stated in GSM (grams per square meter). Most fabric stores unfortunately do not state the weights on their fabrics, while more specialised fabric retailers will be able to give you the specs. For making flats, aim for a natural fibre fabric that is at least 220gsm in weight. The heavier the weight, the more absorbent (but also thicker), it will be.