This This diagram and explaination has been supplied and authorised for use by Maui Ultra fins.
Good question it is the most used material and the choice of the fin maker for the past 20 years or so. G10 was and is used in the electronics industy and mainly used in PCB boards due to its superioir durability,dielectrical strength and resistance to chemical and high operating temparatures. It has been adopted in the Marine industry too because of its superior stability in wet conditions and its impact resistance. G10 is fine weave fibre glass and Epoxy resin laid up and then pressed under weight to produce a dense hard waring laminate. Most blanks produced for Fin making are up to 50% fibre volume giving the density and impact resistance required.

G10 is a superb material to machine with most Fin makers utilizing CNC machine processes to create volume in their production line.
CNC or (Computer Numerically Controlled). Is a process that allows for a material to be cut using a spinning cutting tool guided by a computer program. The tool takes a program and cuts the sheet material or blank into the desired shape. Most of the programs are CAD (computer aided design). In the case of the Fin the program cuts this into sections giving both profile and foil and then cuts this into the blank producing the finished item.
Spin out or commonly known Cavitation is where you fin stalls mainly due to air under the board causing the fin to track sideways at 45 degrees causing drag. This can also be caused by too much back foot pressure giving the feeling of tripping or loosing your fin.