Wood is a natural, versatile material that has been used by humans for thousands of years: 

Composition

Wood is made up of cellulose, a polymer that forms strong fibers, and lignin, another polymer that's typically amorphous. 

Structure

Wood is a hard, fibrous material that forms in concentric layers around a central core called the pith. The lighter area around the heartwood is called sapwood, and the darker central portion is called heartwood. 

Properties

Wood is strong, insulating, and has desirable acoustic properties. It's also relatively easy to work with and gives off a feeling of warmth. 

Uses

Wood is used in many products, including lumber, furniture, plywood, paper, and chemical products. It's also still an important fuel in many parts of the world. 

Sustainability

Wood is a renewable resource, and if forests are managed properly, trees will continue to produce more wood. 

Strength

Wood's strength and stiffness can be affected by a number of factors, including moisture content, temperature, decay, and insect attack. Wood is also weaker when stress is applied perpendicular to the wood fibers. 

Study

The scientific study of wood is called wood science, which began in the early 20th century.