A well fitted kilt, of any material, does not need a third strap. The strap is a left over from when the kilts had a higher rise, when the rise was lowered to the current 2", there was not enough room above the waist to put the second strap. Some want a third belt so it was put below the waist and tugs on the aprons.

I have made kilts from 10 oz, 13 oz, 1nd 16 oz wool, PV, and wool/blends. The fit is from tapering from the waist to the hips and you don't even need a belt to keep the kilt up. Nor do you need the extra belt and buckle.

Do kilts that are not fitted from the waist to the hips require the third belt? Or, is the top buckle enough to keep the kilt snug at the waist?