The knife-pleated skirt, re-introduced to fashion by Alessandro Michele for Gucci a few season’s back, shows no signs of slowing down. The skirts work in solids, menswear plaids or prints.  The key is using fabric — whether lustrous satin, crisp suitings, iridescent organza or lingerie-worthy lace — that is firm enough to hold a pleat yet lightweight enough to achieve the requisite flow.