Nubuck and it takes the signed Ti buckle from the Omega NATO. BTW, the NATO has grown on me because it is a perfect color match to the dial and it is ridiculously comfortable, durable, and unique with the leather lining. Great for daily wearing.
My favourite Speedmaster. I tried this on at Geneva airport a few years back. A joy to wear. It was offered to me without VAT and a discount as well. I stupidly declined............! [nt]