Carbon profiles are rods and tubes of carbon fibre set in a resin matrix. What they offer is an exceptional stiffness-to-weight ratio: a carbon rod barely deflects at all, yet weighs a fraction of a metal one of the same diameter.
That is why they end up as wing spars, struts, tail booms and anything else where the structure has to be light and genuinely rigid at the same time. The surface is smooth and dark, so a length left exposed on a finished model needs no paint to look right. Choosing the material comes before choosing the section: where a member has to be light and genuinely rigid, carbon wins outright, but for anything that will be cut, drilled and glued again and again, the same shapes in timber from wooden profiles and strip or in styrene from plastic profiles and sections are far less trouble.
