Wall panelling.
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Do not use tongue and grove!
No knotty grain in wood!
Minimal plank width is 6 inches! Ideal would be 2×4 foot boards of plywood.
Use plywood sheets and stain, plywood and walnut veneer or walnut plywood.
Ideal stain for panels is Natural Walnut, not Dark Walnut!
Stain has to be ultra matte. No sheen!