Don’t Overstuff Your PolyMailer: How to Avoid USPS Softpack Adjustments | Thryft Ship
📦 Softpack Tips
Don’t Overstuff Your PolyMailer: How to Avoid USPS Softpack Adjustments
Overstuffed or rigid PolyMailers can lose Softpack eligibility — and that’s how surprise USPS
adjustments (APVs) happen. Here’s how to keep packages flexible, avoid unexpected fees, and ship smarter.
By Thryft Ship•Shipping & Packaging•Updated for 2026
If you ship with PolyMailers, this one matters more than you think.
A large chunk of unexpected USPS adjustment charges comes down to how a package feels, not
just how much it weighs. Overstuffed, rigid, or “brick-like” PolyMailers often lose Softpack eligibility —
and that’s when surprise charges show up days or weeks later.
TL;DR
Softpack = flexible and compressible. A PolyMailer can still be “not a Softpack.”
Overstuffing makes packages rigid and more likely to be reclassified.
A good rule of thumb: keep Softpacks ~3 inches or less and clearly flexible.
What Is a USPS Softpack, Really?
A Softpack isn’t just “anything in a PolyMailer.”
USPS evaluates Softpacks based on flexibility and compressibility. Even if you’re using a
PolyMailer, your package can lose Softpack status if it:
Feels rigid or box-like
Can’t bend or flex easily
Is packed too tightly
Bulges significantly at the seams
Why it matters: If USPS reclassifies your shipment, it can lead to
APV (Automated Package Verification) adjustments after the label is purchased.
Why Overstuffing Triggers Adjustments
When a PolyMailer is packed too tightly:
The contents push outward, creating rigidity
USPS machines and manual checks may treat it like a box
The package may exceed Softpack thickness rules
It becomes more likely to be reweighed or remeasured
Even being off by fractions of an inch can be enough.
The “3-Inch Rule” (And Why It Matters)
While USPS doesn’t publish one perfect diagram for every scenario, a practical guideline is:
Softpacks should generally be no thicker than ~3 inches and must remain flexible.
Once a PolyMailer starts to feel stiff or overly dense, it’s at risk — even if the scale weight is correct.
This is why two packages with the same weight can have very different outcomes.
Common Softpack Mistakes We See
Here are a few patterns that cause trouble:
Stuffing bulky items into too-small PolyMailers
Packing folded clothing too tightly
Shipping shoes or denim without enough flexibility
Using heavy-duty PolyMailers that don’t bend well
Taping or compressing the package until it’s rigid
None of these are “wrong” — they’re just more likely to trigger USPS scrutiny.
How to Ship Softpacks Safely (and Avoid Fees)
Size up your PolyMailer
If it feels tight, it probably is. Slightly larger mailers usually keep packages more flexible.
Let items breathe
Fold gently. Avoid compressing everything into a solid block.
Do the bend test
If you can’t gently flex the package with your hands, USPS probably won’t treat it as a Softpack.
When in doubt, switch packaging
For bulky or structured items, a box can be the safer option (and often avoids surprise adjustments).
A Note on USPS Adjustments
It’s important to know: this happens on every shipping platform, not just Thryft Ship.
USPS applies APV adjustments based on their scans and checks — not the platform used to buy the label.
During high-volume periods (like the holidays), incorrect scans can happen more often, especially for
borderline packages.
Best defense: Use clean, flexible packaging from the start. If your Softpack is close to
the line, give yourself a little buffer.
Final Takeaway
PolyMailers are amazing — when used correctly.
Keeping Softpacks flexible, not overstuffed, and comfortably sized can save you money, prevent
surprise adjustments, and make shipping smoother overall.
If you’re ever unsure, remember: Flexible beats tight every time. 💜
