From the review:
The swords come in two colors, and of course they're only fun if you get the set. At $12 for each one, depending on where you buy, this isn't an expensive proposition. They may look like brightly-colored children's toys, but they hold a secret. Each sword isn't just made out of the soft foam that Nerf is known for; a plastic rod runs down the length of the sword. Swinging one in the air makes a satisfying whistling sound, and swords hit the skin of an opponent with a wonderful *THWAP* sound. They're more than tough enough to be beaten against each other time and time again without snapping in two.