Most traditional envelopes use dextrin-based adhesive—a starch glue activated by moisture (that’s the “lick-and-seal” kind). When wet, it flows into paper fibers. As it dries, it hardens into a flexible bond.
Freezing doesn’t melt this glue. Instead, cold makes it brittle. The adhesive loses pliability, its grip on the paper fibers weakens, and—when handled gently—the seal releases like a sigh.
Important note: This only works on water-activated adhesives. Modern “peel-and-stick” envelopes use pressure-sensitive synthetic glues that laugh at freezer temperatures. If your envelope didn’t require saliva to seal, the freezer won’t help.
