Select your spline and shift rotate 90 degrees. Make sure your splines cross over by enabling Enable in Render and Enable in Viewport. The result should look like this (Fig.05).
Convert to an editable poly. As you can see it is a bit messy so let's clean up the mesh to make it nice and uniform (Fig.06).
Shift-drag your nice clean piece of strap and repeat to get a long section of strap (Fig.07).
Almost done. It's now time to add some dimension to this strap. To get the strap to bend round to the cap, use a bend modifier and play around with it to get what you wanted (Fig.08).
To make the strap a little less uniform and make it look more natural, let's use a Noise modifier and change a few of the parameters. Once you're happy with that, use the FFD 3×3 modifier to make it look more relaxed. Here you can see the result of the Noise modifier (Fig.09).
There is no step 10 really. I would advise you to convert the strap to a VRay Proxy once you are done modifying as this strap is quite poly-heavy and might cause some problems if there are a lot of other objects in your scene (Fig.10)
This strap was made for my Hugo Boss model. It could be made for any other model and you can use any modifier you want to get your desired effect.
I hope this tutorial was of use to you - thanks for watching!