Yellow ‘415 Spines -Fins equipped with Yellow spines will have a higher angle of attack of seventy five degrees in the 'toe down' direction. This generally implies that fins equipped with Yellow spines will be easier to kick, yet may require a greater flutter kick stroke length than fins equipped with Blue spines. There is no difference between Yellow spines and Blue spines during the 'toe up' flex direction of twenty degrees. Truefin has had a variety of opinions as to the kicking experience of fins equipped with Blue versus Yellow spines, with some saying Blue spines are better, and others saying Yellow spines are better. As indicated above. there appears to be a correlation between kicking range of motion and preference of spines. For example, users having a long and relatively slow flutter kick may find better efficiency and velocity with Yellow spines, versus users who have a short and relatively fast flutter kick who may have better efficiency and velocity with Blue spines.