We use double braid polyester 1/4" rope for our halters due to its strength, low stretch, excellent sunlight resistance, and excellent abrasion resistance. A double braid rope refers to a braided rope cover over a braided rope core. Basically, it is a rope over another rope. These ropes are often flexible and easy to handle.
The rope comes in soft, firm and stiff. The soft is well liked by natural horse trainers. The stiff is also very popular with trainers and is used in the popular 4 knot noseband training halters. The stiff rope holds it's shape and form well making it very popular. The firm is a great option for those that are looking for the weight of the soft with a little more structure.
Here are the color options for each rope.