Andrew, the last solid that I did was made of green cotton-twill. I prefer the cotton-twill for three reasons.
1).It's more forgiving in the sewing process, which allows the kiltmaker to bend it with their fingers (allowing for better drape).
2).It's tougher than nails in wear and tear. This is my third one in cotton-twill, and there's no fading or wear.
3).There's no pilling or running. I have six poly-viscose kilts and they all are pilling. Two have the fabric seperating in the fibers. Not a happy camper at all.
If you're lucky enough to get a nice, thick cotton-twill, it will get softer with washings (and Downey) while it maintains its form.