Hmmmm.... it could be a lot of things I suppose but an interesting question. The wool in one of my 8rd kilts was woven by Pendleton. Though a tartan, it was not woven specifically for kilt making. It stretches a wee bit when worn but also adjusts back. I have another that is made of a "blended stretch wool" and of course it stretches a bit. None of my other kilts seem to stretch at all, especially my 8yd tank made of pure tight weave scottish wool -- couldn't budge it if one tried! I too lost weight about a year ago and also noticed a bigger difference in the waist of my "dress" kilt than my trousers but then I realized that I wear the kilt a lot higher (just below ribs) than my trousers (between navel and hips) and I just figured I lost more inches from above than below. I also know that I pay a lot more attention to the "fit" of my dress kilt than I do to the others, as I tend to do with "dress" anything as opposed to "everyday wear." Your situation could of course be entirely different ???