Wood wool, known primarily as excelsior in North America, is a product made of wood slivers cut from logs and is mainly used in packaging, for cooling pads in home evaporative cooling systems known as swamp coolers, for erosion control mats, and as a raw material for the production of other products such as bonded wood wool boards and used as stuffing for stuffed animals.
The term wood wool is used in the United States to describe finer grades of excelsior. The U.S. Forest Service stated in 1948 and 1961 that, "In this country the product has no other general name, but in most other countries all grades of excelsior are known as wood wool. In the United States the name wood wool is reserved for only a small proportion of the output consisting of certain special grades of extra thin and narrow stock."
The U.S. Standard Industrial Classification Index SIC is 2429 for the product "Wood wool (excelsior)". The same term is used by the United States for the external trade number under which wood wool is monitored: HTS Number: 4405.00.00 Description: Wood wool (excelsior); wood flour.
The number 4405.00 is applied to wood wool by the World Customs Organization in the Harmonized Commodity Description and Coding System (HS).
Grades and classifications 
The 1973 U.S. federal procurement specification PPP-E-911, cancelled in 1991, categorized "wood excelsior" products according to the following table of terms and dimensions:
TABLE I. Strand size for type I class A and B excelsior ------------------------------------------------------------------------------- Thickness of strand Width of strand Grade Nomenclature Inch Inch ------------------------------------------------------------------------------- 1 Superfine wood wool 0.006 0.020 2 Wood wool 0.012 0.020 3 Extra fine 0.015 0.031 4 Fine 0.018 0.031 5 Medium 0.021 0.041 6 Coarse or ribbon 0.015 0.167 -------------------------------------------------------------------------------
Excelsior is used in packaging, cushioning, for stuffing plush toys or real animals in taxidermy, and for cooling pads in home evaporative cooler systems known as "swamp coolers." Excelsior pads are widely used in the shipping of day-old poultry in the United States when it is placed in the bottom of a cardboard box to cushion the birds while providing some warmth and absorbing waste.
Excelsior, dyed green, makes an annual appearance as the "grass" in Easter baskets, or did in earlier decades before the prevalence of plastics.
Excelsior has other applications, such as mats and blankets for erosion control, garden mulch, dog bedding, hutch bedding, and udder cleaning for dairy cattle. It is also used for the production of cement-bonded wood wool boards.
Banded into bale form, excelsior is also used in archery backstops, comparable to how a straw bale would be used for the same purpose. If protected from the elements, an excelsior archery backstop can last for many years. If sections of it wear down because of repeated targeting, the bale can be soaked liberally since it then expands and holds water, just like a dry sponge.
Wood wool fibers can be compressed and when the pressure is removed they resume their initial volume. This is a useful property for minimizing their volume when shipping. Due to its high volume and large surface area, wood wool can be used for applications where water or moisture retention is necessary. The width of wood wool fibers varies from 1.5 to 20 mm, while their length is usually around 500 mm (depending on the production process).
In the UK there are specifications for dimensions, pH, moisture content and freedom from dust and small pieces, set by British Standard BS 2548 for wood wool for general packaging purposes. This standard was originally issued in 1954 and subsequently re-issued in 1986.
When these fibers are bonded with cement or magnesite, bonded wood wool boards are produced. Slabs of bonded wood wool are considered environmently friendly construction and insulation materials because they do not contain organic binders.
Excelsior is cut from "bolts" (round, halved, quartered, or otherwise split logs) of poplar (for example aspen), pine, spruce or eucalyptus. For evaporative cooler pads, the dominant source is the aspen.
Finally, wood wool can be dyed to produce a variety of colored products.
A different product was once known as "wood wool," as well as "pine needle-wool," or "pine wood-wool." According to E. Littell, it was produced in Breslau, Silesia (today Wrocław, Poland) by von Pannewich, who mentioned that in 1842 five hundred counterpanes made of it were purchased for a hospital in Vienna. The process was chemical and made use of the leaves (needles) of Scots Pine.
In England, yet another product known as wood wool was produced by the chemical breakdown of wood strips by means of sulphurous acid, for use in such applications as absorbent material in surgical dressings. Another application of this product was use in sanitary towels, as shown in advertisements from 1885–1892 in Britain for "wood wool diapers" or "sanitary wood wool sheets". European "wood wool" was known in America in the last nineteenth century as being distinctly different from excelsior.
The wood wool that is the topic of this article is what has traditionally been known as excelsior in the United States. Fifteen U.S. patents related to "slivering machines" for producing the small wood shreds "known as excelsior" were listed in 1876. The earliest, a machine for "Manufacturing wood to be used as a substitute for curled hair in stuffing beds" was patented in the U.S. in 1842; however, the product had no specific name when the process was first patented.
The 1868 patent, "Improved capillary material for filling gas and air carburettors," was for a new use for "fibres torn from the wood by suitable machinery" to be "sold and used as filling for mattresses, its commercial name being 'excelsior'." This is the earliest description of the material by this name cited by the Oxford English Dictionary, though the term "excelsior mattress" had appeared in print as early as 1856.
In 1906, the now-common use of excelsior in the cooling pads of evaporative coolers appeared in a patent that stated, "I have found that excelsior makes a very cheap and good material for this purpose."
In the beginning of the 20th century wood wool was used as a raw material for producing wood wool panels in Europe, especially in Austria. By 1930, wood wool cement boards were being widely produced. 
In the 21st century, excelsior appears in numerous patents for erosion control and sediment control methods and devices; for example, the 2006 "Sediment control device and system." A few late-twentieth-century patents on these uses refer to "excelsior/wood wool."
- U.S. commodity code: Wood wool (excelsior)
- Nelson Courtlandt Brown (1919). Forest Products, Their Manufacture and Use. J. Wiley. p. 425. ISBN 1-145-47804-2.
- W. F Gericke (2007). Soilless Gardening. p. 38. ISBN 978-1-4067-7064-3.
- Forest Products Laboratory (1948). Excelsior manufacture — Original report dated May 1948 — Reviewed and reaffirmed 1961. U.S. Dept of Agriculture, Forest Service.
- U.S. Standard Industrial Classification Index SIC 2429 for "Wood wool (excelsior)"
- HTS Number for Wood wool (excelsior)
- Harmonized Commodity Description and Coding System (HS), page 2, 4405.00 wood wool
- "Federal Specification: Excelsior, Wood, Fabricated Pads and Bulk Form". September 28, 1973.
- E. F. Lindsley (July 1984). "Solar air conditioners — the hotter it gets, the better they work". Popular Science (Times Mirror Magazines): 64–66. ISSN 0161-7370.
- "Mail Order Shipping of Day-Old Chicks". HOWELL FARM. Retrieved 9 March 2013.
- David Daniel (2005). The Marble Kite. Macmillan. p. 35. ISBN 978-0-312-32351-6.
- "The Tradition of the excelsior stuffing". HERMANN-Spielwaren GmbH. Retrieved 24 July 2006.
- Market Analysis of Erosion control Mats United States Department of Agriculture
- Wood wool applications
- Wood wool Cement Boards, Production and use, page 284 in "The Ecology of Building Materials", Bjørn Berge, Filip Henley, Howard Liddell, Architectural Press, 2001, ISBN 0-7506-5450-3, ISBN 978-0-7506-5450-0 
- Jim L. Bowyer, Rubin Shmulsky, John G. Haygreen (2007). Forest Products and Wood Science. Blackwell Publishing. p. 412. ISBN 978-0-8138-2036-1.
- Larry Wise (1992). Bow and Arrow: The Comprehensive Guide to Equipment, Technique, and Competition. Stackpole Books. p. 912. ISBN 978-0-8117-2411-1.
- BS 2548 Specification for wood wool for general packaging purposes (British Standard)
- BS 2548 BSI British Standards
- Wood Based Panels International, Friday, March 1 1996
- European Commission Research - Industrial Technologies, 15/09/2005
- The Black Poplar
- Roger E. Simmons (1912). Wood-using Industries of New Hampshire. I. C. Evans co. p. 53.
- The suitability of Eucalyptus grandis and two provenances of Pinus kesiya for wood wool-cement slab manufacture by A J Hawkes; A P Robinson; Publisher: London : Tropical Products Institute, 1978. ISBN 0-85954-086-3, ISBN 978-0-85954-086-5 
- Gert Jan Bom et al. (1999). Evaporative Air-conditioning: Applications for Environmentally Friendly Cooling. World Bank Publications. p. 25. ISBN 978-0-8213-4334-0.
- ISO 9567:1989 Woodworking machines — Horizontal shredding machines for wood wool production, quadruple effect — Nomenclature
- ISO 9615:1989 Woodworking machines — Vertical shredding machines for wood wool production, with hydraulic clamping — Nomenclature
- "Our wood wool is washed and cleaned to remove as much dust as possible"
- Kiln dried wood wool
- Colored Excelsior
- Peter Lund Simmonds (1858). The Dictionary of Trade Products, Manufacturing, and Technical Terms: With a Definition of the Moneys, Weights, and Measures of All Countries. G. Routledge. p. 288.
- E. Littell (1852). Living Age. Boston: Littell & Co.
- Bertram Blount, Arthur George Bloxam (1905). Chemistry for Engineers and Manufacturers. C. Griffin and Company, Limited. p. 281.
- Wood wool diapers, 1885-1895 advertisements
- Advertisement for "sanitary wood wool sheets", 1895
- H. A. Hare and Edward Martin (editors) (1897). Therapeutic Gazette Series III Volume XIII. Detroit: William M. Warren. p. 242.
- Edward Henry Knight (1876). Knight's American Mechanical Dictionary: A Description of Tools, Instruments, Machines, Processes, and Engineering; History of Inventions; General Technological Vocabulary; and Digest of Mechanical Appliances in Science and the Arts 3. Hurd and Houghton. p. 2214.
- Wm. Baker (1842). "Machine for manufacturing wood so as to be used as a substitute for curled hair in stuffing beds". U.S. patent 2654.
- John A. Bassett (1868). "Improved capillary material for filling gas and air carburettors". U.S. patent 60670.
- Michigan State Agricultural Society (1856). Transactions of the State Agricultural Society of Michigan: With Reports of County Agricultural Societies, for the Year 1849-59, vol. 7 (1855). p. 139.
- John Zellweger (1906). "Air filter and cooler". U.S. patent 838602.
- New strands to the wood wool story Botting, Mike in Wood Based Panels International, June 1, 1997
- Peter S. Sanguinetti (2006). "Sediment control device and system". U.S. patent 7021869.
- Erosion control blanket and method of, U.S. Patent 5786281, Jul 28, 1998