This photo speaks for itself. I got this nice piece of 1/4" walnut at the local hobby shop. They have lots more like it. Walnut is softer than hard maple - 1010 vs 1450, but otherwise similar in strength - 1.7 vs 1.8. I've read a lot on the internets about walnut fretboards, and come to the conclusion that 90% of it is BS - know-nothings stating their suppositions as facts, or repeating standard luthier nonsense.