ticking and seep through into lower layers. In addition to being unhygienic, hard to launder, and unsightly, such stains typically void a warranty. Thus a mattress protector is suggested to protect the mattress; this can be removed and cleaned separately, and replaced if damaged. Industry Companies often specialize in a particular type of mattress, such as innerspring, latex, and airbed, although as latex and airbeds have become more popular, they have become more common. United States of America Mattresses which are mostly the same are often sold under different brand names; two of the largest brands, Serta and Simmons, became owned by the same company after a private equity buyout. Simmons, founded in the late 1800s, was bought and sold multiple times and faced bankruptcy after a major decline in the bedding industry in the 2000s. The International Sleep Products Association was founded in 1915 and releases a report on U.S. mattress sales. Another association, Specialty Sleep Association, represents companies such as Innomax and Boyd Specialty focused on latex, waterbeds, and airbeds. However, Select Comfort, which produces airbeds (a specialty bed), is a member of the ISPA. Originally founded in 1881, the Sealy Corporation was purchased by Tempur-Pedic in 2012, which had introduced an all foam (TEMPUR-Material) brand into the United States in 1992. Adjustable beds have become a trend and are more compatible with certain types of mattresses such as latex or memory foam. These are particularly popular in Europe, and for one business accounted for 25% of beds in Sweden in 2010 and 70% of beds in the Netherlands. In the 2010s, affiliate marketing became a major part of the business model for direct-to-consumer online mattress companies such as Amerisleep. Later, companies like Casper and Purple, with venture capital and funding followed and helped grow the global mattress industry to $28.5 billion dollar in 2018. According to experts, there are over 175 bed-in-a-box mattress companies in the United States. Mattress suggestion methods are emerging in response to the crowded retail marketplace. Another large company, Spring Air, went bankrupt in 2009 and was purchased by one of its former executives. Comfortaire, founded in 1981, was the first to specialize in airbeds. It was later bought by Select Comfort. Spain Pikolin, founded in 1948, is one of the largest manufacturers of mattresses. See also Bed frame Duvet International Sleep Products Association Law label the "Do Not Remove Tag Under Penalty