The biggest factor that I can think of is simply fabric weight. And there is more to it than just the ounces per yard of the fabric. I mean the total fabric weight of the cloth incorporated into the pleats. Simply put, the more fabric used, the heavier it is, the more the pleats will swing. This is why, all other factors being equal, a 6 yard kilt will swish more than a 4 yard kilt, and an 8 yard kilt will swish more than a 6 yard kilt. All that weight in the back acts like a penulum when you walk. The heavier that pendulum, the more movement you will get.