The primary structural material used in the cell walls of plants is cellulose.

Here's a bit more information:

* Cellulose: This is a complex carbohydrate made up of long chains of glucose molecules. It forms strong, rigid fibers that give plant cells their shape and support.

* Other components: While cellulose is the primary component, plant cell walls also contain other substances like hemicellulose, pectin, and lignin. These components contribute to the wall's strength, flexibility, and ability to interact with the environment.

Let me know if you'd like to learn more about plant cell walls!