Black fiber strip. At 63" these strips can go around the perimeter of most guitars so that only 2 are needed. Most of the manufacturers have been using fiber for a few years, and of course, it's a staple in violin making. Fiber, like maple, doesn't compress so it leaves an even line but sometimes it's a little difficult to level it to the top or back with a scraper. Harry Fleishman always gets creative in his designs; here he's inlayed the back of his koa harp guitar with white/black/white strips.