I wore a four-yard kilt every day for five months, in rain, snow, sleet, hail, and gallons of sweat. I never ironed it, and the pleats remained true. Only the very first pleat to the left of the apron "softened", because the four-yard kilt required that it was shallow. If there had been a bit more material it would have been deeper, and no problems at all (on my eight-yard kilt, that first pleat is much deeper).

Andrew.