I got some construction Perlite one time for $11a bag. It was medium size and perfect to mix with Medium bark for orchid media. As a safety precaution, it was always pre wetted to avoid the fluoride. http://www.pacificbulbsociety.org/list.php Joyce E. Miller Sacramento, California, USA USDA Zone 6 Gresham Oregon, just east of Portland Oregon in the Willamette Valley