Technically, it is possible to install new wallpaper over existing wallpaper, but it is generally not recommended for several reasons. 1. If the existing wallpaper is textured or has any bumps or ridges, it can create an uneven surface that will make it difficult for the new wallpaper to adhere properly. This can cause the new wallpaper to bubble, peel, or come loose over time. 2. If the existing wallpaper is not properly sealed or is damaged, it can allow moisture and humidity to seep through to the new wallpaper. This can cause the new wallpaper to become discolored, warped, or even moldy. 3. If you install new wallpaper over existing wallpaper, it can make it more difficult to remove the wallpaper in the future. Removing multiple layers of wallpaper can be a time-consuming and messy process that can damage the wall underneath.