I have made several "sheaths" (scabbards actually) out of nylon webbing :
www.seattlefabrics.com
www.ahh.biz.
WEBBING:
I got supplies of widths 1/4", 1/2", 1", 1&'/2", 2" and 3". There are various weights and weaves to choose from but in general nylon webbing is much stronger than cordura or even ballistic nylon and the edges do not have to be doubled over. Loose ends may be doubled over and/or heat sealed. Heat sealing is very effective but looks ugly. Many combinations can be achieved with the various widths.
SEWING:
Most sane people use a heavy duty sewing maching but I do it all by hand, sometimes using a small craft pliers to push the needle through. I use heavy duty polyester thread but the thinnest needle I can get away with for easiest penetration. A needle threader is a must. Many needles get broken.
LINER & ASSEMBLY:
Pockets and attachments must be made beforehand and sewn on before affixing the webbing to the stiff liner........I make the liner with 1/16" thick polycarbonate sheet (Lexan). I cut an appropriate size piece, heat (not overheat) it with a heat gun and shape it in a vise with the help of pliers until it closely fits the blade with a slight friction fit and no rattling. The resulting liner has a sharp fold at the blade's edge and is open at the spine of the blade but extending slightly past the spine. Holes are then drilled and the and the open part is lashed closed with stainless steel fishing leader. The blade should fit neatly into the liner and stop at the handle. I leave about 1/2" extra at the tip for safety. The liner will be completely covered by the webbing so it doesn't matter if it is not cosmetically perfect. I have only used polycarbonate but, from what I read, Kydex might just as good and easier to work with.
I glue the webbing (with presewn pockets and attachments) to the liner using Goop brand glue. It can be messy but really grips the webbing and polycarbonate. The webbing should cover the front and back of the liner and extend as far as you want up the handle and stll have enough length to double back down for a belt loop. So you might need about 22" of webbing for a 6" liner.
SOME DETAILS:
The width of the webbing must be chosen so that the sides of the webbing extend at least 1/2" beyond the sides of the insert. The glue must not be applied to the overhang but only the part of the webbing touching the insert so that the needle goes through more easily. After the glue dries, sew the sides of the webbing tightly together. Experience has shown me that sewing alone will permanently hold the insert in place because the webbing will be stretched over the slightly raised fishing leader, but I use glue for perfect positioning before sewing.
FINISHING
Now you have your basic sheath with about double the length of the knife handle hanging free from the back (side facing the body). It has on it, pockets, loops, attachments, etc. You now sew the belt loop. You can sew it direct or use velcro and/or snaps; Or a variety of belt attachments available commercially. Sew on the keeper with velcro or snap and you have yourself a rugged quiet, versatile sheath, highly resistant to ever being punctured by the knife.
Things you might need:
Vise
One sixteenth polycarbonate sheet or Kydex equivalent.
Snaps (I like "Lift the Dot" snaps)
Heavy duty Velcro but not the sticky back kind. Two inch wide rolls are good.
Plenty of webbing in all widths.
Plenty of needles, threaders and thread.
Small craft pliers.
Stainless fishing leader.
Sharp scissors
Compound leverage snips.
Goop
Heat gun:- Optional but makes permanently bending the polycarbonate much easier.
Patience
Probably, a good, heavy duty sewing machine.
I don't know if my way is the approved way but anyway, that's how I do it. I would love to post a pic but am still in the stoneage of virtual reality. I hope this gives you some ideas.