Short answer
Check you peeled off the right layer (usually the one numbered 1), then clean the screen with an alcohol wipe to remove oils and old residue. If the adhesive side has been touched, covered in lint, or reused several times, replace the protector.
Causes and fixes
| Cause | Fix |
|---|---|
| Wrong layer removed | Many protectors have numbered layers; the adhesive is under layer 1 |
| Oily screen | Clean with alcohol wipe, then dry with microfibre |
| Old adhesive residue | Isopropyl alcohol on microfibre until the screen squeaks |
| Touched adhesive | Fingerprints stop bonding; try tape to lift lint, otherwise replace |
| Reused protector | Adhesive loses grip after several lifts; replace |
| Cold room | Warm the phone and protector to room temperature |
Film vs glass
Glass adhesive grabs almost instantly on a clean screen. Some TPU films are fitted wet and take hours to bond; they can look unstuck at first. Follow the film's instructions and give it a day.
Questions people ask
Why won't my new screen protector stick?
Usually the screen isn't fully clean, or the wrong backing layer was removed.
Can I make a used screen protector sticky again?
Not reliably. Cleaning lint off with tape can help once or twice; after that, replace it.