The Koosh ball is a toy ball made of rubber filaments (strings) attached to a soft plasma rubber core. The Koosh ball was developed in 1986 by Scott Stillinger to be easy for his daughter and son (5 and 8 years old respectively) to hold and throw. It was named after the sound it made when it landed. Stillinger started the OddzOn Products Inc. company with his brother-in-law, Mark Button (who had previously been a marketing manager for Mattel), in 1987 in order to sell it. The Koosh ball was one of 1988's hot Christmas toys, appealing considerably to all ages. The company later expanded their product line to include 50 other Koosh-related products, including keyrings, baseball sets, and yo-yos. The number of Koosh Balls sold is estimated to be in the millions.