Residual angular power spectra of the CMB temperature fluctuations from Planck-18 assuming a mixed DM model with varying hot-to-total DM fractions (coloured lines) and a thermal particle mass of m_hdm = 10 eV (left), m_hdm = 30 eV (middle), and m_hdm = 100 eV (right). Note that the blue line (f_hdm = 0) corresponds to the ΛCDM model. The grey error bars denote the 68% confidence interval of the Planck-18 TT data.