Wool insulation is made from sheep wool fibres that are either mechanically held together or bonded using between 5% and 20% recycled polyester adhesive to form insulating batts, rolls and ropes. Some companies do not use any adhesives or bonding agents, but rather entangle the wool fibers into in high R-Value, air capturing knops (or balls) that hold themselves together. Natural wool insulation is effective for both thermal and acoustic insulation. The wool is often sourced from the less expensive black wools of the UK and Europe. Batts are commonly used in the walls and ceilings of timber-frame buildings, rolls can be cut to size for lofts, and ropes can be used between the logs in log homes. Wool knops are installed loosely in attics or in walls as a blow-in-blanket system utilizing a fiber mesh to hold the wool in place during the blow in process. Natural wool insulation should be distinguished from mineral wool insulation, also called slag wool or rock wool, which only resembles natural wool fibers. It is actually made from rock, blast furnace slag, and other raw materials which are melted and spun into fibers. Sheep wool is a natural, sustainable, recyclable material, which is biodegradable, and has low embodied energy. It does not endanger the health of people or the environment, and does not require protection to install, unlike fiberglass insulation. Wool is a highly effective insulating material which performs better than its rated R value because it can absorb and release moisture. Mongolian nomads used felted and woven sheep wool pads as an insulating layer on the walls and floors of their dwellings, called ger or yurts. The use of wool for insulation is starting to rise in popularity. It is already popular in Australia, which produces 55% of the world's raw and processed wool, as well as in Europe and Canada, and is gaining ground in the United States Building considerations Wool insulation commonly comes in rolls of batts or ropes with varied widths and thicknesses depending on the manufacturer. Generally, wool batts have thicknesses of 50 mm (2 in) to 100mm (4 in), with widths of 400 mm (16 in) and 600 mm (24 in), and lengths of 4000 mm (13 ft 4 in), 5000 mm (16 ft 8 in), 6000 mm (20 ft) and 7200 mm (24 ft). The widths of 16 in and 24 in are the standard measurements