Up until not too long ago, downhill skis were of very simple construction. They began as planks of wood. Later on metal edges were added to better grip the snow and ice of a ski trail. Through the 1970s and 1980s, with many composite synthetic materials becoming available, skis got stronger, lighter, and more supple (which enabled better turning). In the mid-1990s, manufacturers began producing "shaped" skis (when viewed from above or below, the center or "waist" is narrower than the tip or tail) for use by the mass market and by slalom competitors. Shaped skis are less efficient at straight travel (because they compress a wider track in the snow, compared to similar-length straight skis), but they are easier to turn. Direct downhill racers still use straight skis for speed.
By setting the ski at an angle so that the edge cuts into the snow, the ski will follow the arc and hence turn the skier, a practice known as carving a turn. Straight skis can be used to carve turns, using the flexibility of the ski to produce an arc, but it is easier with shaped skis. Influenced by snowboarding, during the 1990s this shaping of the ski became significantly more pronounced to make it both easier for skiers to carve turns, and to dramatically increase the turning sensation experienced. Such skis were once termed carving skis, or shaped skis or parabolic skis to differentiate them from the more traditional straighter skis, but nearly all modern recreational skis are produced with the curve.
