Things You'll Need
Mug of water
Envelopes often accidentally become stuck when high humidity levels activate the gum adhesive on the envelopes. When an envelope is stubbornly stuck and you must unstick it, there are several ways to solve this problem using simple household appliances. Once you successfully unstick the envelopes, they should adhere again normally when you are ready to use them.
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Set the iron to low heat. When the iron is warm, run the iron over the sealed envelope to warm it slightly. Insert the tip of the knife between the two layers of the envelope to separate them. Slide the knife along the edge of the envelope flap to separate the flap of the envelope.
Set the iron to low heat. Moisten the clean cloth slightly with water. Wring it out well. Place the damp cloth over the envelope and place the warm iron over the cloth. Leave the iron on the cloth for two seconds and remove the iron. Insert the tip of the knife between the two layers of the envelope to separate them. This method may work better for more stubbornly stuck envelopes because it utilizes moisture to unstick the envelope flap.
Place the stuck envelope into the microwave oven. Place a mug of water in a rear corner of the microwave to add moisture to the microwave. Turn it on and run it for up to 20 seconds. Remove the envelope and open the flap. It should unstick easily.
Place the stuck envelope into the freezer. Leave the envelope there for up to 24 hours. Remove the envelope from the freezer and insert the tip of the knife between the two layers of the envelope to separate them. The extreme cold and dryness of the freezer should unstick the envelope.