The type of rope that I like to make my rope tack with is PNW Select Rope. There is a reason why the professional horsemen use it, just as a carpenter uses high quality tools, they do not want their "tools" to break, fatigue, etc while in the middle of a job.
True, rope halters do not break...unless, you are using the cheaper types from China, such as a lower quality fiber...like the ones you get at the hardware stores. Their utility ropes break at 400 - 600 lbs. They also do not hold up to UV rays (which horses are always exposed to the outdoors) or to the weather (rain, snow etc). Which breaks down the fibers...I've been doing a lot of research on this...
When I have asked several of the professional trainers, why they like the polyester over the other fibers...they kind of gave me a funny look...the majority responded with: "It lasts longer, more resistant to the sun and weather, withstands uric acid (urine), will not absorb water or urine as much as nylon (nylon absorbs 15 - 30% moisture, which in time creates a stiff rope) polyester only absorbs 5 - 12% moisture. Also, polyester will not stain and can be washed".
Nylon Stretches, absorbs moisture, etc. While polyester has low stretch, extremely low moisture absorption and is more resistant to all the elements the horse industry can throw its way.
So, again, the professionals are correct...I contacted PNW Select Rope to see if the guys/gals were right...once again...science supported the pro's statements.
I found PNW Select Rope (in 17 different colors) through their dealers. If you want to buy it in cut lengths, it is available through Mountain Supply, or if you want it in bulk, there is Sunset Halters, Many Miles Designs or Hardware Sales.
Again, true about the rope halters that do not break. However, if you have tied the appropriate safety knot on your lead rope, you would be saving your horse from a wreck...Rope halter or webbed halter.
Oh, and by the way...I've seen just as many horse deaths from horses wearing a webbed halter too. Horses should not be turned out with any halter. The last horse I saw that died, was scratching her jowl with her hind leg...her hoof got caught up in the webbed halter...she fought and fought, fell over, broke her neck and spine...and still could not get near her to help. They had to shoot her.
Therefore...if you are using good judgement on your tack and take any safety advice the professionals tell you, you should be Good to GO