There are several types of liners, to harvest stool in the cloth diapers, or for a stay dry effect.
As the name suggests, these liners are disposable (in the trash) after use. Do not throw them in the toilet, because despite what can be mentioned on the packaging of certain brands, these liners can clog the pipes and are difficult to treat at the wastewater treatment.
Some of these liners can be washed a few times when they have not been in contact with stool.
Note that disposable liners do not have a stay dry effect (if you use them in a cloth diaper that has a stay dry effect, this stay dry effect will be cancelled by the liner). They can therefore cause irritation.
Most often in micropolar or polar, these liners are very useful to bring a stay dry effect in cloth diapers that are devoid of them. They are commercially available, or can be easily manufactured by purchasing polar or micropolar fabric (100% polyester), or by recycling an old plaid, or other garment (beware of the dyes used, if you do not buy a fabric specially designed for cloth diapers). All you need is a pair of scissors. The fabric does not fray and therefore does not need to be sewn.
They are also very useful when using a zinc-based cream, as they avoid stains in cloth diapers (disposable liners are too thin for this use).
The wool liners:
These liners are perfect for a stay dry effect, while avoiding synthetic materials. The wool absorbs a little moisture which adds a stay dry effect AND a small extra absorption. You can also knit them with pure wool (merino for example, which is soft) untreated.
They are also bought all made, made of woollen fabric, sometimes with an addition of synthetic fibers (up to 3% for those I have seen) which allows to wash them in a machine. Which is very nice. They also exist in 100% wool, but are more delicate at maintenance.
This is great news for people who choose natural materials, and still want a stay dry effect.
Wool liners used for the stay dry effect should not be lanolized.