The Cabot's Quilt insulation behind the partition wall of this California home is rich in history, though it's of limited value as an insulator.

A remodeler encountering a layer of Cabot's Quilt inside an old building might mistake it for the tattered remnants of a Hawaiian grass skirt - hastily stuffed into a wall, perhaps, during a police raid of some Prohibition-era costume party. The reality is only slightly less surprising: It's an early insulating material made from dried eelgrass (a marine plant harvested from beaches in the northeastern U.S. and adjacent Canada) stitched between sheets of heavy paper. Beginning in about 1900, it was distributed nationally and heavily advertised in trade publications by its manufacturer, Boston-based Samuel Cabot Co. Today, with precious few...