Combined chemical structure of pre-DD RLOF components of DD II and DD III type systems. Indicated are the masses of He-rich (M_He,acc, M_He,d) and CO-rich (M_CO,acc, M_CO,d) layers of both the accretor and the donor star for both DD II and DD III type systems. The horizontal black line indicates the Chandrasekhar-mass. We note that only masses higher than 0.6 M_⊙ are shown for legibility.