A board’s flex can vary along its length, often stiffer in the tail for better edge hold and snap, but softer towards the nose making it easier to float in powder. This is known as ‘directional flex’. On the contrary, boards designed to ride backwards just as well as forwards will boast ‘twin flex’, which is exactly the same in the nose and tail.
‘Torsional flex’ is less commonly discussed, and refers to the stiffness of a board from one side to the other (if you were to twist it). However, it does play a role – torsionally stiffer boards will be quicker to transition from edge-to-edge and are better at holding carves, while softer boards are better suited to everyday riding and freestyle.