The density of wool refers to the amount of wool fibers per square inch. High-grade sheepskin, like that of Overland's premium Australian sheepskin rugs, has a very high wool density, largely due to the breed of sheep it comes from. Also important is the wool's loft, or its ability to stay upright and straight. A lower quality sheepskin rug may flatten quickly, or its fibers may become curly, tangled or matted, whereas high-quality rugs boast wool fibers that retain their loft beautifully.