Many many pocket diapers and All In Ones use microfleece as the layer that touches the baby. The reason is that it is soft and it doesn't absorb moisture so the wetness passes right through to the hidden absorbant layers, leaving the baby feeling mostly dry. I'm contemplating making up a bunch of AIO's for my next little one, in which case I will probably use microfleece as the inner.
Some moms, however, don't like to use it in a pocket or AIO. There are a few reasons why:
- since it touches baby's tender skin, some prefer it to only be a natural fiber like cotton/bamboo/hemp/etc.
- on a hot day, wet cotton might be more comfy for baby than dry but hot microfleece.
- synthetic materials tend to have problems with soap build up over time and can result in stinky diapers that are higher maintenance because they need to be stripped every so often to get the stink out.
I think it is somewhat of a personal preference and what you are comfortable with.
HTH! Someone else can probably explain better than me, though!