Polypropylene swords are known for their durability and impact resistance. Polypropylene is a tough and rigid thermoplastic polymer that offers good strength and resilience. When used to create training swords, polypropylene provides a solid and sturdy construction that can withstand repeated strikes and impacts.

The hardness of a polypropylene sword can vary depending on the specific formulation of the material and the design of the sword. Polypropylene swords are generally rigid and resistant to bending or warping, but they may have some flexibility to absorb and distribute impact forces.

Polypropylene swords are designed to provide a safer alternative for training and sparring, as they minimize the risk of injury associated with sharp-edged swords. They are less prone to breakage or damage compared to wooden swords and can withstand regular training use.

However, it's important to note that polypropylene swords are not as hard as steel blades. They do not have the same edge retention or cutting ability. Polypropylene swords are primarily used for developing technique, practicing forms, and engaging in controlled sparring or partner drills.

Overall, the hardness of a polypropylene sword is a result of the material's inherent properties and the specific design and construction of the sword. The focus of polypropylene swords is on impact resistance and durability rather than replicating the hardness of a real sword.