As the kirtles without a waistseam, I've also experimented a fiew different construction theories for this type of kirtle as well. We have quite a few exemples of high resolution images where details can be made out in the most surprinsing way and yet, none of these show definate lines that would clearly point to a specific construction. This image is amongst those that are the neatest. This is thought to be a kirtle made of grey squirrel bellies, cut in small patches and assembled in order to create a full skirt. Therefor, there are no specific guidelines to follow as this is somewhat of a "patch-work" job. What we are seeing is the leather side of the fur. This further supports the theory that this was in fact an undergarment as this specific kirtle was also depicted in other scenes such as the "Saint Colomba triptych" where it's indeed worn as an undergarment. I don't believe that this kirtle is covered with additional fabric as some have speculated, I think that the teeny seam allowances is simply directed on the fur side and so, are hidden by the hair. You can definatly get the certainty that this is indeed grey squirrel fur (petit-gris) by the reversed guard of the skirt.