sentences:  Low-end department or toy store skate frames may be composed of other types of plastic.Speed skate frames are usually built out of carbon fiber or extruded aluminum (more expensive but more solid), magnesium, or even pressed aluminium, which is then folded into a frame (cheaper but less sturdy).Carbon fiber frames are expensive but generally more flexible, making for a smoother ride at the expense of worse power transfer between the leg and the wheels.