Thread for stitching heavy cotton

I've got a linen haversack from Jas Townsend but after one season, it's unraveling. I was wanting to make a replacement out of heavy canvas or cotton duck, trimmed in leather. The body of the bag would be fabric but the trim and attachment points, along with the strap will be leather with brass hardware and antler buttons. What would be the strongest thread to use for stitching the cloth together? I've looked at heavy duty cotton, polyester and silk threads but don't have a clue which would work best. Would silk be the toughest?

 

[necchi]

When I'm using my Machine or hand stitching small items where I'm interested in long lasting strength along with the ability to withstand the weather extremes and, not worried about the PC police the thread is the commonly available;
Coats and Clark Upholstery thread
And for canvas the "Natural" color is a perfect match.
This is the stuff found in most Fabric shops and box stores in that multi colored rack/stand.
You gotta look towards the bottom of the rack to find the "Upholstery" thread.
The Upholstery thread is 100% Nylon and has a tensil strength well above 40#, you ain't gonna grab that thread and break it in your hands, it'll cut you before it breaks.

If PC police and stitch counters are a worry then it's Artificial Sinew for this guy.
You can get Linen thread from suppliers but I've never bothered, and never been hassled about my thread choices.

 

[George]

I have made two bags similar to what you describe, a haversack made from a sort of knobby homespun-style canvas and a game bag made from a smooth dense burlap type. Each was sewn with linen/flax thread which I waxed with beeswax as I sewed. Both were made 12-15 years ago, they have been used hard and put up wet, as they say, and I've never had to make a single repair to either of them. If you choose to do it with the old materials and do it right, you don't need to worry about it not lasting.

Haversack:

Game bag:

Spence

 

[Jaeger]

Good lookin' bags, Spence! Seems I always like your stuff. I plan on sewing up some heavy canvas haversacks, maybe even a half-leather, half-canvas shooting bag and then treating them with linseed oil.

 

[BillinOregon]

Spence, ditto on what Jaeger said. Your stuff is the nuts.
Craig, an excellent source for linen thread of light through heavy 6-strand is Susan Wallace, who owns the Silver Shuttle in Memphis. I just bought hanks of 4- and 6-strand linen thread from her, as well as three bags of tow. You won't find a nicer, more helpful vendor for this stuff.

 

[Rifleman1776]

Good all cotton or flax thread is often hard to find. I have come to much dislike the artificial sinew. It looks artificial and is hard to knot.
But 'certain' shops sell hemp cord. It can be unraveled into various thicknesses and is very strong. Looks 'authentic'. I hand stitch and draw over beeswax to ease the stitching process.

 

[Short Arm]

8/4 cotton rug warps thread and coat it with bees wax.