Killer culatta oil horsehide leather, just the right thickness - not too thin but comfortable and supple. Sueded distressed patch on the left inner heel, you can oil this so it darkens if you don't like the distressed look.
Soles and heels have been Vibrammed by one of the only cobblers in town I trust to work with these (he maintains the balance of the heels and doesn't grind down the sides to retain the original aesthetic). Rubber has a ton of wear left.
Tagged EU43 but fits a TTS US11/EU44. I use FEIT veg tan bullhide insoles in these and wax the bottoms so they don't squeak when you walk - they make these much, much more comfortable than regular A1923s with the super narrow and hard stock insole bottom.