i sed regular printer paper on the inside... i bought a light cream color which matched the card stock cover. i printed it out once and then photocopied it doulbe sided to save ink and also so it wouldn't bleed through, which it will on regular paper.
I'm using parchment paper from Staples. It's a pale marbled blue that goes well with my cobalt blue cardstock covers. I bought a box of 100 sheets for about $12. I'm printing the pages on my color laser printer by printing all of the first sides, then reinserting the pages and printing on the second sides. I've tested it out and it works well. You can't see the text through the paper at all.
