A fine yarn’s weavability is greatly influenced by its yarn size. The manufacture of fabrics and ecological load is significantly impacted by the primary and secondary sizing agents, as seen from the environmental conservation perspective. In actuality, textile sizing and desizing processes generate between 50 and 80% of the COD (chemical oxygen demand) load in textile effluent. Modern sizing procedures are centered on many criteria in the current environment, including low COD size options, sophisticated control systems for reproducibility, ideal quality, and ease of handling. The intrinsic physical qualities of the sized yarn may be enhanced, and the quantity of sizing material used may be substantially reduced by pre-wetting technology, precise measurement systems, and individual drives. To comply with environmental protection regulations, green size must meet the functional needs of warp sizing and attenuate air and water pollutants by sizing with low wastewater, pollution, and toxicity levels within specified limits. This chapter covers the evolution of yarn sizing techniques and newly available sustainable substitutes.