Individual fiber components are blended in accordance with the properties of a required intermediate product such as a card sliver or an end product such as a yarn. The fiber bales are combined into component groups and the fiber components in the groups are accurately supplied by metering devices to a blender in which the components are uniformly mixed. The product from the blender may be cleaned and thereafter carded into a sliver. The characteristics of the sliver, such as the color, fiber, fineness and quantity, are tested and adjustments made in the blending in dependence upon any deviation from preset values for the characteristics.