Elmer’s Products Inc, the owner of the popular U.S. school glue brand, is exploring a sale that could value it at close to $400 million, including debt, according to people familiar with the matter. Berwind Corp, the investment vehicle of the wealthy Berwind family that owns Elmer’s Products, has hired investment bank Robert W. Baird & Co to explore a sale, the sources said this week. Elmer’s has annual earnings before interest, taxes, depreciation and amortization of around $53 million, according to the sources.