They are literally driving me crazy because their style is pretty hard to upholster! But in the meantime, I was asked to upholster another chair seat that is much easier to do and it took me about an hour to make it.
This kind of seat is very common so I hope this Instructable will be useful to you!
Before I started to work on this seat, I removed everything that was around it because it was broken, so all that was left was a wood frame. In case yours is fine and all you have to do is covering it, go to Step 4.
Step 1: What you need
Fold the beginning of it so that it can't break and, using the staple gun, attach it to about one half of the wood frame, as you can see in the pictures.
The webbing must arrive to the other side of the frame so cut it where the wood ends.
Pull the webbing as tight as you can and secure it with a few staples leaving a couple of cm (0.78 inches) free.
Like you did at the beginning, fold the end and attach it. The only difference is that it will be upside down but don't worry.
Do the same on the other half of the frame.
Now rotate the frame and repeat the same process so that there will be 2 new strips perpendicular to the first ones.
You can twist them like I did (see the pictures) but it's not really important.