The most important element on the supply side of the industry was raw wool. Throughout the period it remained by far the greatest prime cost for most firms not specialising in weaving or finishing only. Estimates from the 1850s indicate that wool accounted at that time for between a third and a half of total costs, and between a half and two-thirds of prime costs for worsted manufacturers. The woollen branch must have been broadly similar. Thus wool trading practices particularly the extension of credit by suppliers, formed a major influence on the amount of variable capital needed by the manufacturer.

The bulk of wool consumed by the West Riding textile industry throughout this period was of domestic origin, bought either direct from the growers or, more usually, through factors. Even in 1850 it is variously estimated that as much as two-thirds of the raw wool absorbed by the British woollen industry as a whole came from the domestic clip. However, from the late sixteenth century, changes in commercial agriculture, particularly the spread of enclosures and the cross breeding of sheep for mutton, resulted in the progressive deterioration of the English fleeces in most counties. English wool grew longer and coarser which made it admirably suitable for combing and worsted production but much less suitable by the late eighteenth century for the woollen industry, especially the finer products. The industry responded by increasingly mixing the finer and softer Spanish and German wools with the domestic clip, and by the late 1820s many woollen manufacturers were using as much, if not more, of these imported fibres than the English wool.