Lee Valley, one of my favorite innovative woodworking tool makers and retailers, is now selling a variety of items — wallets, totebags, pouches — made from what they call Tree Leather (TM).
Tree leather is what the rest of us call paper.
I purchased a small bag, and played with it a bit. Like a paper bag it is highly puncture resistant, and for a fairly thick .023″ does not seem to delaminate internally when repeatedly folded. Tear strength is good, but not exceptional, roughly on par with vegetable tanned leather this thick. The surface pH is quite low, 4.5.
Lee Valley describes the tree leather as being made from long fibered kraft paper, and I bet there is some polyethylene added as a protective coating, giving it the washability they tout.
It is not a huge surprise to anyone involved with books or conservation that paper is quite durable and strong. In fact, many book conservators tend to view leather as a cosmetic, not structural aspect when repairing a binding.
But it is an example of how the notion that leather is strong and durable, and paper is weak still persists. This despite being challenged in print for over 100 years. See Viscount Cobham and Sir Henry Trueman Wood Report of the Committee on Leather For Bookbinding (London: Published for the Society of Arts by George Bell and Sons, 1905.)
Peachey Conservation 
I also wondered whether there was some coating or ingredient added to give the stuff wet strength (it absorbs water, but isn’t weakened by it.) I emailed Lee Valley, who emailed the manufacturer. Here is what they told LV: “Thank you for your inquiry. Tree Leather is industrial-grade kraft paper. It is not bleached or impregnated with anything. The strength comes from the process. The fibers are left “long”, which provides a natural strength and resilience to the paper – even when wet. These products are not necessarily water resistant. The bags and wallets will absorb water, but the paper stays as strong wet as it is dry.” Also, the little card in the photo says the stuff is “100% Kraft Paper.”
It seems like the stuff would make an attractive cover material for a soft book. Too bad it is so acidic.
Thanks! I guess if you are making books for short term use the acidity shouldn’t be a huge problem.