This document discusses eco-friendly building materials. It defines eco-friendly materials as those that cause minimum damage to the environment from raw material extraction through the final product. Key properties of eco-friendly materials are that they require minimum energy for manufacturing, are recyclable and reusable, and are locally available. Examples discussed include bamboo, mud bricks, fly ash bricks and plywood made from agricultural waste. The document also explores how to determine if a material is truly eco-friendly based on factors like availability, embodied energy, and potential environmental impacts.