Why do metal window frames sometimes cause the window glass to crack on cold days?

Metal window frames can cause the glass to crack on cold days due to the difference in thermal expansion and contraction rates between the metal and the glass. When temperatures drop, metal frames contract more than the glass, creating stress at the interface where they meet. This stress can lead to cracks, especially if the glass is already under tension or has imperfections. Additionally, if the metal frame is poorly insulated, it can exacerbate the temperature difference, increasing the risk of cracking.