The shelf life of commercial envelopes—especially gummed #10 window envelopes used in mailing equipment—is typically 12 to 18 months under proper storage conditions. After this period, you may begin to see degradation that affects performance, including:

Key Risks After 12+ Months:

• Seal failure: The envelope gum (glue) can dry out, crystalize, or lose tack, leading to poor or failed sealing during high-speed insertion.

• Warping or curling: Humidity changes can cause the paper stock to warp, making envelopes jam or misfeed in inserters.

• Window film issues: Window adhesives may become brittle or delaminate, and static buildup may increase.

• Dusting or offsetting: Coatings or inks (if printed) may deteriorate and affect rollers or create feed issues.

Best Practices:

• Store envelopes in temperature- and humidity-controlled environments (ideally 68–76°F, 35–55% RH).

• Rotate stock regularly—first in, first out (FIFO).

• Conduct a test run on your inserters before using the batch for a large job.

• Check glue integrity by manually sealing and unsealing samples from different parts of the pallet.

If these envelopes have been on your floor for over a year and exposed to variable conditions, it's smart to test a representative sample immediately. 

✅ Envelope Quality Assurance Checklist

📦 Visual Inspection

• No visible warping, curling, or bowing of envelope flaps or bodies

• Window film intact and fully adhered (no bubbling, peeling, or static issues)

• Glue strips appear uniform and not discolored or brittle

• No signs of mold, dust buildup, or paper aging (yellowing, brittleness)

🔧 Manual Function Tests

• Seals properly with light moisture (if gummed) or pressure (if self-seal)

• Window placement aligns with insert content properly

• Can be opened and resealed cleanly without tearing

• Flap folds and returns to original position without resistance or stiffness

🧪 Inserter Equipment Test (Sample Run)

• Feeds smoothly in high-speed inserter (test ~100 envelopes minimum)

• No jams, double feeds, or misalignments

• Glue activates and seals properly under machine conditions

• Window holds up under rollers (no tearing or static clinging to inserts)

📋 Documentation

• Record date received and length of storage

• Note any deviations from original specs (e.g., humidity exposure, open packaging)

• Capture test results and note issues by batch or box number