Sealing Envelopes and Packages
You may not give much thought to the act of sealing up an envelope or package, but that doesn’t mean it’s a trivial step in the mailing or shipping process. We’ve created this FAQ to answer all the questions you may have about sealing shipments before handing them over to the USPS.
What’s the right way to seal a box?
According to USPS, you should tape the opening of your box and reinforce all seams with tape that is 2 inches wide.
What kind of material should I use to seal a box?
You’ve got a few options—USPS says you should use clear or brown packaging tape, reinforced packing tape, or paper tape.
Packaging tape—plastic, pressure-sensitive tape is easy to use, readily available, and versatile. It easily adheres to multiple surfaces, so can use it to seal boxes as well as poly mailers.
Reinforced packing tape—this tape contains fibers that make it stronger and a good option for heavier shipments.
Paper tape—also known as kraft tape, uses a water-activated tape dispenser (water is what helps bond the tape to the boxes). Paper tape sticks to cardboard but doesn’t adhere to poly mailers or other non-paper surfaces.
Is there anything I can’t use to seal a box?
You should refrain from using twine, cord or string—these materials can get caught in the mail processing equipment. You should also avoid using masking or cellophane tape, as they’re not strong enough for this purpose.
Can I use extra tape to reinforce an overly full USPS envelope or box?
When sealing Priority Mail® or Priority Mail Express® Flat Rate boxes and envelopes, the container flaps must be able to close within their normal folds, according to this USPS publication. You can use tape on the flaps and seams to reinforce the envelope or box, but you cannot reconstruct the packaging in any way.
How much tape is TOO much tape?
When using a Flat Rate Envelope or Flat Rate Box, using tape as a reinforcement on the seams and flaps is OK in order to keep the item from breaking open during transit. Encasing a box or envelope is NOT OK. No matter what packaging you use to ship, using too much tape can cost you in more ways than one—first, you’re using up your supplies faster than necessary, plus the extra weight from excessive tape could push you up to a higher weight category.
Can I use tape to affix a shipping label?
Anyone shipping with a PC Postage label (we’re talking about you, Stamps.com customers!) can use extra tape to properly attach a printed label to an envelope or box. However, you should avoid covering the barcodes on a USPS label, as the tape creates a glare that can make it hard for barcode scanners, thus messing up your tracking. Sick of taping labels to packages? Visit the Stamps.com Store to order adhesive labels.