HOW MUCH CARBON CONTENT DOES A WINDSURFING MAST NEED?
NICE, EASY AND LIGHT
Of course, a higher content also means a lighter mast, with more control and earlier planing and acceleration advantages too.
Naturally no mast can be made 100% of carbon, so the quoted carbon percentage represents the carbon content aspect only, as the other materials used - such as resins and protective tapes - are not included.
STRENGTH AND VALUE
Lower carbon content gives two main advantages. Cheaper masts and actually stronger masts in many cases too.
However, along with price, the sensations are also reduced - while weight is increased - resulting in a 'deader' action from lower responsiveness.
Sails will always perform best on the higher percentage models and, especially on freeride/freerace and [camber-induced] race sails it's always wiser to match your sail with the best mast that you can afford.
Many would also argue that, by using 100% carbon models, you'll break less masts by being able to plane earlier and avoid trouble in the surf too.
But for strength, especially in say, wavesailing, 80% can be a good mix of durability and performance. (Bear in mind that using the shortest mast you can in a sail allows you the chance to decrease vulnerability to breakages and still use a reactive, 100% carbon mast, but that using a mast shorter than recommended can also soften your rig and affect sail shape. Not a bad thing, just choose wisely considering your build, sailing conditions and preferred style etc.)
Another issue to bear in mind for maximizing durability, especially in waves, is to consider sails with lower luff curve, so the mast is under less tension to start with.
QUALITY CONTROL
Various brands' manufacturing processes also affect the performance.
For example, a pre-preg (pre-impregnated with resin for reliable, consistent layup) 60% carbon content mast can perform as well as another brand's non pre-preg 80% model.
Generally speaking, 'performance' can be gained from 60-80% models upwards, while 30 or 40% models can be a good fit for intermediate/progression sails (although a little heavy for smaller riders) or sails with very low luff curve (so the mast has less influence on sail shape).