Stiff base and flexible tip using carbon fibre inserts - carve faces, stay tight in the pocket. Very nice set of quads - we like them for our Hipster Pilchard - but they work well on any quad. Available in Small to medium sizes (for 65 to 80 kg surfers) AP1 or Medium to larger (75 to 90 kg surfers) AP2. Its the side fins that are different - similar base but the AP2 has about an inch extra depth. Now if you are 75kg then you could go either way!