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Owens Corning FOAMULAR 150 appears to be available in CA.
Very nice job, love the use of common materials, stax are opaque, so easier than jars. How big should the seedlings be? Have you tried coir/coco husk or moss instead of (problematic) rock wool?
Link is broken, but it's at https://web.archive.org/web/20100606061223/http://modati.com:80/lasercutter/