The nato straps are 30cm long and 1.5mm thick.
They have been woven like canvas, and contain a little bit of cotton to make them feel softer and look a bit more vintage.
You can put them in the washing machine, they come out clean and even softer. The buckles are connected with a push pin, so you can put a clasp of your watch brand on the strap.

(4 Ways to wear your watch on a nato, on YouTube)