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.
Thickness Vs Density
Different fabrics have a different thickness and density. It is important to realise that there is a difference between “thickness” and “density” when we are talking about fabrics used for padmaking. Thickness is just how much space a fabric takes up. Density is how tightly packed together the fibres are. So the thicker a fabric is, does not necessarily mean it is better or more absorbent. The fibres are what absorbs liquid, not the air around them. So a “thick” airy fabric won’t be as absorbent as a dense thinner fabric.
A good example of this is “batting” used for quiltmaking. This fabric is light and fluffy as it is designed to trap air inside and that air gets heated with body warmth and that keeps your quilt warm. But pads need to hold liquid, not air. So while the fibres in batting may be made from cotton or bamboo, the fabric is not designed to absorb liquid, it is designed to trap air. A fabric like bamboo fleece is thinner but more importantly has a lot more densely packed fibres. It is designed to absorb liquid. There are also differences in the composition – Quilts aren’t made for monthly laundering whereas pads need to be, but that’s a different discussion :)
The density of a fabric is measured in “GSM” (Grams per square metre). This is a measure of the comparative weight of the fabric, and gives an indication of how dense the fabric is. For an absorbent core fabric, the more fibres packed together and the higher the GSM, the more dense the fabric is and the more absorbent it will be. So a fabric with a 400gsm will have twice as much fabric in it as a 200gsm fabric. You may not be able to see or feel much difference between them, but the absorbency will be different.
You want your pad cores to be dense and absorbent, not just “thick”. Getting the right absorbency in a thinner core is preferable to having a thick bulky core, because as with the quilt, if it’s thick because it’s trapping air, it will make the pad feel hotter.
Value for money (pay more, cut less)
Sometimes it is better to buy a more absorbent and more expensive fabric that you will use less of, than to buy a cheaper less absorbent one you will use more of. Not only because the cost of the cheaper fabric might end up being more expensive when you have to use more of it, but also with the extra time it takes to cut.
Thin fabrics like flannel/flannelette seem like a good choice because they are thin, absorbent and cheap – but as explained above, the absorbency in a fabric comes from the density and thickness.
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.
For example – one layer of a 400gsm bamboo fleece is probably about the same thickness of 2 layers of flannel, but you need about 3 layers of flannel to achieve the same absorbency as 1 layer of the bamboo fleece. So that will be thicker and more cutting. Sometimes it can be quicker and cheaper to buy a more absorbent fabric you need less of. If you are selling your pads be aware that most customers prefer bamboo fleece or zorb cores over something like flannel – as they know it’s a more suitable fabric.
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.