The quality attributes of the top determine, or limit, the quality of yarn and the performance during spinning. Most modern spinning mills have similar machinery, and if the settings and maintenance are up to standard, then the yarn properties are primarily determined by the fibre properties of the top and the linear density and twist of the yarn.

The properties of the top are determined by the greasy wool properties and the quality of topmaking but we can reliably predict spinning performance and yarn properties from the measured top properties without reference back to the greasy wool.

For any yarn made up from staple fibres the key determinants are the average number of fibres in the yarn cross-section, the mean length of the fibres and the mean strength of the fibres. The average number of fibres is very important because we cannot control the position of each fibre and the variation in the number along the yarn, as a percentage of the mean, is much bigger when there are only a few fibres. Thus the evenness of the yarn and the likelihood of thin places is dependent on the number of fibres and hence on the diameter of the fibres. The yarn strength is dependent on the number and severity of thin places, the strength of the fibres and how well they are bound together to share the load. The binding depends, in turn, on the twist and the length of fibres.