Progress in package‐dyeing yarn during the past ten years has been rapid, both in the total weight of yarn dyed, the types of fibre being dyed, and particularly in the design of dyeing machines and to a lesser extent in dyeing techniques. Polyester filament yarn is of great importance, but there have been significant developments in dyeing high‐bulk acrylic yarns. In machinery developments, the outstanding features are in the rate of flow of liquor, and the frequency with which the liquor is circulated. New techniques have been developed to take advantage of these mechanical features, so that dyeing can be commenced at 135°C and the liquor dropped at this temperature, thus minimizing oligomer problems with polyester yarn. Many new disperse dyes of high sublimination fastness on polyester fibre have been introduced and these take full advantage of the new machinery and dyeing techniques.Another factor leading to wider use of package dyeing has been the need for shorter manufacturing cycles in the production of coloured yarn, particularly for woven fabrics. Worsted yarn, which would normally have been spun from dyed top is now being package dyed on a large scale.With spun yarns, the advantages of dyeing acrylic yarn in muff form have led to the rapid growth of this method of dy