Plastic is generally harder than wood. This is due to the molecular structure and manufacturing processes of both materials. Wood is a natural material composed of cellulose, hemicellulose, and lignin, which gives it a relatively soft and fibrous texture. On the other hand, plastic is a synthetic material made from polymers, which can be engineered to have varying degrees of hardness.

According to the Rockwell hardness scale, a common method for measuring the hardness of materials, the hardness of wood typically ranges from 1.2 to 2.5 on the scale, while plastic hardness can range from 20 to 100. This significant difference in hardness is due to the synthetic nature of plastic, which allows for the creation of materials with specific properties, including increased hardness.

For example, high-density polyethylene (HDPE) has a hardness of around 70 on the Rockwell scale, while oak wood has a hardness of around 1.5. This means that HDPE is approximately 46 times harder than oak wood. The ability to control the molecular structure of plastic during the manufacturing process allows for the creation of materials that are much harder than natural materials like wood.

In addition to the molecular structure, the manufacturing process also plays a role in determining the hardness of plastic. Plastics can be reinforced with materials like glass fibers or carbon fibers to increase their hardness and strength. These reinforcing agents can significantly enhance the hardness of the plastic, making it even more durable than some types of wood.

In conclusion, plastic is generally harder than wood due to its synthetic nature, the ability to control its molecular structure, and the potential for reinforcement. This makes plastic a preferred material in many applications where high hardness and durability are required.