Using molecular dynamics phonon wave packet simulations, we study phonon transmission across hexagonal (h)-BN and amorphous silica (a-SiO 2 ) nanoscopic thin films sandwiched by two crystalline leads. Due to the phonon interference effect, the frequency-dependent phonon transmission coefficient in the case of the crystalline film (Sijh-BNjAl heterostructure) exhibits a strongly oscillatory behavior. In the case of the amorphous film (Sija-SiO 2 jAl and Sija-SiO 2 jSi heterostructures), in spite of structural disorder, the phonon transmission coefficient also exhibits oscillatory behavior at low frequencies (up to $1.2 THz), with a period of oscillation consistent with the prediction from the two-beam interference equation. Above 1.2 THz, however, the phonon interference effect is greatly weakened by the diffuse scattering of higher-frequency phonons within an a-SiO 2 thin film and at the two interfaces confining the a-SiO 2 thin film. Published by AIP Publishing.