I just wanted to post the steps that I take to make shoulder straps for my backpacks.
The materials I used are:
-4mm foam mesh from Rockywood or you could use 3D mesh from thru-hiker
-330d Cordura
– 3/4" Grosgrain
-3/4" webbing
-3/4" Ladderlock
The first thing I do is mark out the pieces I need to cut on the back of the fabric. I cut a template out of mat board to make this task easier. You will need to cut 4 straps out of the foam mesh, 2 facing to the left and 2 facing to the right. I also cut out a left and right strap from the cordura. I use the cordura to give the straps some extra strength, you could by all means leave the cordura out.

Next I Take all the pieces that I cut out and separate them to their proper sides. You will want the backs of the foam pieces together with the piece of cordura in between them as shown here…
Once the pieces are together I sew them together

I then add a strip of either grosgrain to webbing about 9" up from the bottom curve of the strap. This works good if you use a water bladder to keep your tube in place.
Next I attach the grosgrain trim. I first measure out how much I will need and cut the proper amount. I then fold the grosgrain in half and put a crease down the middle the length of the strip. This makes it much easier to make sure you have the edge of the strap in the middle of the grosgrain. I then start on one end and sew the grosgrain on the whole way around the strap. The curve of the strap can be tricky so take your time.


I then change out thread, I use a nice complimentary color of heavy tread and add my ladderloc and webbing.
here is the underside of the strap 
I then continue to bar tack the whole way up the strap to the top. I leave about 6" between the ladderloc and the first bar tack to attach a chest strap. I then continue to add bar tacks every 2.5" to the top of the strap.


And that is pretty much it. When you attach the strap to the pack I make sure to run a couple of bar tacks over the webbing so it is sure to hold. The webbing is the strongest part of the strap, the other material just disperse the weight of your pack. Here is a few closeups of the strap attached to the pack.

So this is how I make my straps. I hope this will be useful to anyone thinking about making a pack. They are really fun to make, they just take some time planning. If you have any questions about any of the steps please feel free to ask!
Chris
I like the strap to be around 2.5" wide 21" long. I have found that the bigger or harder the curve to the ladderloc, the better the straps lay with a chest strap attached. But hey give it a try and see what works for you that is all part of the fun!
