Okay so a simple sleeve would be slimmer, but "Second Slimmest" doesn't have the same ring to it. Two pockets in contrasting colors. This will hold some cash and some cards. As you use it more, it will stretch and accommodate a few more, but this is really for those times when you might otherwise just slip your necessities into a jacket pocket for a night out. Or for someone who has the most dialed in of minimalist EDC.
Horween Chromexcel leather.
Natural Vegetable Tanned leather tanned in the US. This will develop a beautiful patina over time and evolve from the light tan to a darker, reddish brown as its exposed to light, oil, dirt, sweat and whatever else you subject it to.
Italian made waxed, braided polyester thread originally developed for sewing shoes. It's solid stuffed and saddlestitched by hand.
Edges finished and burnished by hand.