The higher the OITC score, the better a window is at lessening sound transmission. Traditional single-pane windows with wood or vinyl frames have an OITC of 19. Batt insulation is OK too. Slash the insulation to suit, and use non-long term adhesive like duct tape to carry it in place. https://carolinef059yup6.gynoblog.com/29436173/noise-reduction-benefits-of-acoustic-windows-no-further-a-mystery