Exactly what purpose does the parachute itself serve? I know it offers good visibility of the fly, and it gives you something to wind the hackle around, but am I correct in saying that it shouldn't have any bearing on the fly's flotation? I only ask because the first few parachutes I tied with poly yarn posts had a tendency to drop completely under the surface, especially if there was any disturbance in the water. At first I thought it was because of the post material and switched to calf tail; now I'm thinking it was because I didn't wind enough hackle on those flies, and that's why they wouldn't float well. So does it matter whether I use poly yarn or calf tail if my only concern is to keep the fly in the film?

Best,

Dave