ADDITIONAL FACTSUpdated a year ago

1. MAST STIFFNESS

Your rig is like a bird's wing, it is not a static but a dynamic object. Everything above your boom is under permanent movement to react/adapt to changing wind conditions (wind strength and direction) as well as to water movement.
There is a simple rule across all masts: the longer the mast the stiffer it is, or rather, the stiffer it must be. This is simply because the larger the sail surface becomes, the more support it needs from the mast. In a way the mast is the backbone of your rig.
What happens if a mast is too stiff or too soft for the sail (size)?
1. mast too stiff: the rig becomes super hard to control (especially when powered up) and uncomfortable (exhausting) to sail as the mast doesn't flex sufficiently e.g. when a gust hits your sail.
2. mast too soft: a mast that is too soft reduces the profile in the sail (because it already bends too much when downhauling the sail). When sailing It also bends too much with every gust. Both factors reduce the performance of your sail.
Your body weight also plays a role here. On the same sail a 60 kg lightweight will want to use a slightly softer mast than a 90 kg heavyweight sailor.

2. MAST DIAMETER (RDM VS. SDM)

There are two diameters existing:
1. SDM (Standard Diameter Mast) with 48,5 mm inside diameter at the bottom
2. RDM (Reduced Diameter Mast) with 32-33 mm inside diameter at the bottom 
RDM masts make sense only up to lengths of around 430 cm, as they have a rather soft flex behaviour due to their smaller cross section. Therefore, they are primarily suitable for Wave/Freestyle sails with the additional advantage that they are easier to grip during manoeuvres.
On the other hand, larger, mostly performance-oriented sails require stiffer masts with a “more direct“ flex. This characteristic requires a larger mast cross section in order to achieve the required stiffness. 

3. CARBON CONTENT >< WEIGHT >< PRICE >< PERFORMANCE

Compared to glass fiber, carbon is

1. a much stiffer fiber:
   Due to this higher stiffness, less material/wall-thickness is requires, which ultimately results in a much lighter mast. The weight of the mast has an significant influence on how light the whole rig feels in your hands. No joke compared to a 50% carbon mast with a 100% carbon mast your rig will feel as if it would be 1 square meter smaller! And this is something everyone from beginner to World Cup pro will immediately feel and appreciate.
    

2. a much faster reacting (responsing) fiber:
   When a gust hits your rig it twists off to absorb the sudden energy surge (instead of pulling you into a catapult). In order to create forward movement the mast has to reflex back. The faster this happens the faster the rig is ready for the next gust/impact.
    

3. a much more expensive fiber:
   Unfortunately carbon fiber is 10-20 times more expensive than glass. That means the higher the carbon content, the more expensive the mast.