For many years we have experimented with a variety of loop materials for stinger loops as used for Intruder style flies. Historically braids are popular, in particular Spider Wire. However, all braids have the characteristic that they soak up water and become too limp to keep the hook in line with the shank. This is a common cause of solid bites that do not hook up; the hook dangles too low. The other alternative is stainless steel, plastic coated wire. This keeps the hook nicely in line but has some other issues; the plastic coating tends to break down and the junction area with the hook starts to rust. It eventually becomes a weak point and fails. Thirdly, nylon loops of different varieties are used; mostly ordinary tippet material or shooting line. Again some issues with this; nylon tends to stretch and warp, particularly round nylon. Many nylons are too soft and do not keep the hook in line with the fly. Rio’s slick shooter is a popular stinger material and is a good example of a nylon that is too soft for this purpose.
We utilize an oval, relatively hard nylon, that we custom dye. The oval hard nylon that we use allows the hook to ride perfectly in line with the fly and does not kink under stress. We have tested this loop material for many years and have found no flaws or failure.
Here is a good instructional blog on how to secure loop material to a shank: