Flex

Flex refers to the extent to which a weapon bends when struck against a rigid object. For all weapons other than javelins, a weapon is not allowed to flex more than 45° in a single direction. Javelins are allowed to flex up to 90° for safety.

The degree to which a weapon will flex is almost entirely a result of the core material chosen and the length of the weapon, although the extent of padding and the balance will also affect it to a lesser degree. A blue sword built on a 3/8" fiberglass core, for instance, will fail for flex if the core length is significantly over ~27", while one built on a double core or 1/2" fiberglass core will never fail for flex. Weapons built on a bandpole core have almost no flex at all, with only the heaviest of hammers able to make the core bend significantly.

For more information, see Checking Weapon Flex and Category:Core Materials.