The guinea pigs typically found in pet stores grow six to ten inches long and usually weigh two to four pounds. Their appearances may vary significantly, however, because breeders have developed many different types of domestic guinea pigs. Many of these breeds are primarily distinguished by their hair type. English and American breeds, for instance, have hair that is smooth and short, while the hair of Peruvian varieties is long and coarse. A wide array of hair colorations also exist among guinea pigs, and some breeds are even distinguished by rosettes, whorls of hair radiating from a center point, or the satiny sheen of their coat.