After trying many options, I've settled on what I believe is the best leather possible for wallet interiors. The correct leather must be thin enough to not add needless bulk to the wallet, but rigid enough to hold its shape and work with. I found lightweight Chromexcel or Latigo to be just too soft. Hand dying vegetable tanned leather worked, but was difficult to match colours consistently. Not wanting to compromise on the quality of the product, I worked directly with the tannery Wickett & Craig. Originally from Toronto, and now located in Pennsylvania, Wickett & Craig is the premiere vegetable tanned leather producer in North America. I found a weight of English Bridle that was perfect for the wallet interiors, and had them make me the leather to match all of the colours that I offer.
All bifolds, front pocket wallets and iPhone wallets will use this leather for the interior (other than natural vegetable tanned wallets)
The following photos show a 6 card bifold with a Burgundy Chromexcel exterior and a matching English Bridle interior. The beauty and consistency of the English Birdle can clearly be seen.