Sealing an envelope and then realizing you forgot to put something inside can be frustrating, especially when the envelope contains an important check, letter, or private message. Fortunately, an old-fashioned method may sometimes allow you to reopen the envelope without completely damaging it. While it is not guaranteed to work, it can provide an opportunity to correct the mistake.

The freezer method works best with traditional lick-and-stick envelopes that use water-based adhesive. Placing the sealed envelope in a freezer can make the glue more brittle and weaken its hold. After chilling it, the flap may be easier to lift carefully. If you try this method, patience is important, as forcing the flap could easily tear the paper.

The technique does not work on every type of envelope. Modern self-adhesive envelopes often use stronger adhesives that may not respond to freezing in the same way. Even with traditional envelopes, the paper or adhesive can tear during the process, meaning you may still need to replace the envelope.

Sometimes the flap may open relatively cleanly, while other attempts could leave visible damage. The method simply takes advantage of how certain adhesives and paper materials can react to low temperatures. If you accidentally seal an envelope before adding something important, this simple trick may be worth knowing—but it is best to handle the envelope gently and be prepared for the possibility that it may not work.