These are the most common reasons why the window film doesn't stay up:1. The backing paper isn't removed. There is one even if it doesn't look like one. It's clear in colour.2. The film is touching the edges somewhere. If it does, air will appear underneath and it will lose it's cling. It's safest to leave a minimum of a 2-5mm gap so it doesn't touch the window seal.3. The window film is applied to a textured glass. If it is, air will come underneath and it will lose its cling. Instead use a self-adhesive film for those surfaces.4. The glass has already got some kind of film on it (e.g. UV protection / tint etc).5. Not enough water has been sprayed on the glass surface during application. The more the better to achieve a better cling. Then make sure you squeeze out as much water as possible and let the sun burn off the rest. (Maybe keep the window closed for a day or so until the sun has done its part)6. The wrong side of the window film is facing the window. Make sure it's the cling side. It's nice and smooth.7. The windows are not properly cleaned before application. Make sure they are cleaned from grease and dust. This goes for the film too if it's being reapplied or has been applied to a not fully clean window.