Swiss and German bamboo rod makers Philippe Sicher and Christian Trixner presented and studied various methods to make hollow rods. The cavities of the rod can assume different shapes and so create different geometric sections, notably:

• Magic Star
• Fluted
• Powell
• Reim

The purpose of hollow rods is the reduction of weight, yet a compromise must be reached otherwise the action of the rod will be affected, although this is still a topic at the centre of a debate an opinions vary drastically.

So, their conclusions were:

• The biggest weight saving are with longer rods
• The ferrule area must be solid (weakest fracture point)
• The glue applied does not affect the rod construction i.e. it does not fill the cavities. However, care must be used and a small brush used
• The action of the rod IS affected but this is left to the personal judgment. On this regard, they prepared 5 identical rods (identical taper, a Garrison 209E, 8', #5) and varied the internal structure, from full to Magic Star, Fluted, Powell and Reim hollow-methods. The biggest weight loss was with the Fluted method (-15.6%), followed by the Magic Star (system preferred by Philippe Sicher, - 12.2%), Powell (-7.2%) and Reim (-6.1%).

I think this is a very well presented topic and a good introduction to hollow-buil rods in bamboo.

Incidentally, IBRA (the Italian Bamboo Rodmakers Associations) also created a special hollow-built rod based on Roberto Pragliola's - Italy most influential fly angler - flycasting style and called it IRP. This rod,opened up an intersting topic on the tolerance in bamboo rod making.

By tolerance we man the following. If you want to measure the diameters of each section of the finished rod in order to see if the final result complies to the parameters set on paper in the beginning, you notice that simply the humidity in the airinfluences so much those same parameters that it's impossible to make such rod within the set measures!

from Philippe Sicher and Christian Trixner's presentation to the Sansepolcro Gathering main page