The global fashion and textile industry significantly contributes to economic growth, culture, and consumer lifestyles but also heavily impacts the environment through intensive resource use and pollution. It accounts for more than 10% of the global carbon emissions (270 kg/person of carbon emission in 2020), with serious social and health consequences. Fibre is the primary material of the textile industry; therefore, if we would like to reduce the environmental impact of textile industry, it is essential to understand the environmental footprint of the fibres used in the production of textiles. This chapter provides an in-depth exploration of textile fibres used in fashion and textile, including natural (plant and animal-based), synthetic (man-made cellulosic and synthetic polymers), and recycled or bio-based emerging materials. It examines the historical evolution, production processes, geographical distribution, and technical properties of these fibres. The environmental footprints of various fibres are critically reviewed using Life Cycle Assessment (LCA). We will assess these and highlight hotspots such as resource extraction, energy consumption, water use, chemical discharge, greenhouse gas emissions, and microplastic pollution. Additionally, the chapter evaluates contemporary sustainability efforts, including fibre recycling technologies, bio-based innovations, and their associated environmental trade-offs. Through a comprehensive analysis of material lifecycles, the chapter underscores the complex relationship between fibre selection and ecological responsibility, advocating for harmonized Life Cycle Assessment methodologies and systemic improvements in sustainability practices.