Fin Efficiency

A fin is never at the base temperature all the way to its tip, so it delivers less than an ideal surface: η = tanh(mL_c)/(mL_c). Long, thin, low-conductivity fins are inefficient — past a point, extra length adds almost nothing.

Efficiency above ~90% usually means the fin could be longer; below ~50% means it is too long, too thin, or the wrong material.