The thermal conductivity, measured by the 3ω method, of amorphous films of Al 2 P 1.2 O 6 (AlPO) deposited on Si substrates by an all-aqueous spin-coating technique is 0.93(3)Wm −1 K −1 . The thermal conductivity of a degenerately doped n-Si substrate is 85(5)Wm −1 K −1 and of a more lightly doped p-Si substrate is 139(7)Wm −1 K −1 . The AlPO thermal conductivity is independent of film thickness in the range 45–200nm. The total thermal resistance is dominated by the film contribution for film thicknesses above 50nm, and for smaller thicknesses, interface contributions become significant.