On the double built rods there's 2 layers of bamboo... in the butt section anyway
On the interior, the sections are planed to a pie shape like normal. Then there's a second layer glued over that of the "powerfibers"
That's the way I understand it anyway
It makes for a hefty rod
The #25 is easily a 7wt. Unusual for a 7'6"
And I believe that was the shortest rod that SB made at the time.