Summary: A new synthesis of Mg-Al double hydroxides is described, that gives products relatively low (0.8–1.0%) in CO₂. The general formula [Mg_1−xAl_x (OH)₂][(OH)_x(H₂O)_0.81−x] with 0.23 ≤ x ≤ 0.33 is proposed. Cell parameters and thermal data are given. The c-axial length decreases with Al-content; this is attributed to increased electrostatic attraction between layers.