NATO and ZULU straps are constructed out of nylon. They are very similar both in design and in function. There are three main things you should consider when comparing or buying them.
1. NATO has an additional piece of the strap underneath the watch (two pieces in total) which prevents it from dropping when you take it off. ZULU is made from one unique nylon strap.
2. ZULU strap has rounded keepers (loops) and an oval-shaped buckle. NATO strap has slimmer metal keepers (loops) in rectangular shape or with slightly rounded corners.
3. With a NATO strap, the buckle is positioned outwards the wrist and can't be centered under it. With a ZULU strap, the buckle can be centered under the wrist.