Wool care consists mostly of lanolin, natural wool grease removed from wool in the early stages of processing. With this, you'll make your wool garment dirt and water repellant. It's like a hair conditioner to wool.

When wool is on sheep, it's very greasy, as this helps the sheep be hygienic and warm. When wool is prepared for textiles, almost all of the grease, known as lanolin, is washed off and collected for later use. For wool high-stress wool garments it's sensible to restore some of the greases, as this makes the wool's surface resistant to water and all kinds of things. Good for all kinds of items that experience bad weather, like old wool military overgarments, caps, gloves, jumpers that you use outdoors and what have you. Not all wool garments require wool care - you definitely do not want to use it on your business suit - and regular stuff like underwear might well be okay by using just high-quality wool washing detergent, as that leaves some grease on wool too.