Ok how about i throw it down for every kid who has fucked up their answers in this thread.
Wood core is the orignial core. It is not really heavyer then foam core. It all depends on the type of wood, the type of contruction, and how it is sealed/stained. The common types of woodcore are canadian hard maple, poplar, bamboo, and well basicly mostly any kind of wood if you want to. Differernt woods have different flex patterns.
Bamboo is know to be every light flexible and strong. The only thing is that this wood tends to lose is stiffness very quickly.
Maple is strong, heavy, and can be very stiff depending on the treatment. It is the most durable of all the woods, and the prime wood used in many lumber products ( skateboards, furniture, etc). This is the most commonly used wood in skis.
Wood is prefered because it is stonger and the elements do not change it as easily. The only problem with wood is that if you chip away too much of your top sheet and moisture gets in it would warp the wood resulting in delam, weakness in the whole ski.
Now from what i know about foam ( which is not much, but i have owned a few skis Atomic tweak and 2000 -2002 Salomon 1080 Vinny D).
I found that it is lighter, but alot less durable depending on the ski. My foam core 1080 is in way better shape then my newer woodcore AR5s, but the atomic tweaks are past the point of even being used for urban. The ones i have tryed are quite brittle, and the consistancy of the core will change with the elements. Ive seen some friend's cores melt, expand, and delam their skis due to the skis coming in from the cold to heat. But don't knock foam. Ive seen people who live by it, and there are TONS of old 1080s that are still being used.
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Skiers have genetically bigger cocks......its science