sorry this is a bit late...i've been busy with my new LO
i've actually been making our own CD's so I'll tell you what I know:
inserts you need an absorbant material such as terrycloth, flannel, microfiber (you can get the microfiber towels from walmart's automotive section but they CAN NOT touch baby's skin...they will dry it out), bamboo fleece or other bamboo materials, hemp, etc.
polar fleece wouldn't be a good idea because it repels water so it wouldn't let the moisture seep thru. microfleece is a "stay dry" material...it let's moisture thru to a soaker but allows baby's bum to feel more dry so it is good for a liner type material.
the bamboo and hemp are great, but you have to buy them online at places like nature's fabrics or kidsinthegarden and they can be kinda pricey. I bought 1 yard of bamboo fleece to try out and it was around $10...i've been making some inserts out of them...great absorbancy but it needs to be prepped a lot (washed on hot and dried multiple times before you use it, same with hemp.) I normally combine materials honestly..i'll do a stay dry topper and some flannel or microfiber and then some bamboo. I've been hanging out here: http://community.babycenter.com/groups/a4718385/cloth_diaper_sewing_101?
i think you have to "apply" to be part of the group, but it's not a huge deal. they have a ton of info on sewing your own cloth diapers and inserts and such. hope that helps