The inside of the pad needs to be made from something absorbent, to soak up the flow. This can be a sewn in “core” (As with an AIO), or can be removable insert (Such as with a pocket pad). You will need to use the right absorbency for your flow, so some fabrics will be better suited to you than others.
Sometimes it is better to buy a more absorbent fabric that you will use less of, than to buy a cheaper one you will use more of. This part will determine how thick the pad is overall, and if you like thick pads, then that’s fine, but if you would like to keep your pads as thin as possible, then the absorbency needs some careful thought. Thin fabrics like jersey and flannel/flannelette seem like a good choice because they are thin – but the absorbency in a fabric comes from the thickness and density. Basically the more threads in your fabric, the thicker or more tightly packed those threads are, the more absorbent the fabric will be. Also what the fabric is made of. For example – one layer of a bamboo fleece is probably about the same thickness of 3-4 layers of flannel, but the bamboo would probably be up to 3 times more absorbent. Plus if you are using several layers of something thinner, you’re cutting out all those extra layers, and adding up all those extra costs – sometimes it can be quicker and cheaper to buy a more absorbent fabric you need less of.
When looking at the absorbency of different fibres, it is important to remember that different fabrics have different levels of absorbency. Hemp is more absorbent than cotton, Bamboo is more absorbent than hemp. “Zorb” and microfibre/microterry are more absorbent than bamboo, but these can work like a sponge and may “compression leak” (pooling of liquid) when they are too full – so it is generally advised to team these up with a natural fibre to help hold the liquid in.
Also different fabrics have different thicknesses, for example bamboo fleece comes in various weights, such as 250gsm and 400gsm. The “gsm” means “grams per square inch” – so the higher the number, the thicker and more absorbent that fabric will be.
You don’t have to have the whole winged shape being in a thick absorbent fabric. Instead you can use a smaller amount just down the centre of the pad, which is more cost effective but also makes the wings less bulky.
While these fabrics can be used as the core of a pad, some of them can also be used as a top fabric too. Particularly in the case of “overlocked’/”serged” pads, where fabrics such as hemp and bamboo can be dyed and used as both the top and hidden internal layers.