Actually, you don’t need a box at all — that’s one of the key benefits of the Penguin Mailer.

The Penguin Expanding Insulated Mailer is designed to ship on its own, without requiring an outer carton. Once expanded and sealed, it forms a durable, insulated shell that protects your temperature-sensitive contents in transit. It supports direct label application and is crush-resistant enough for carrier handling.

However, if you still prefer or are required to use an outer box (for stacking, added discretion, or specific carrier requirements), we recommend choosing cartons that are:

• Slightly larger than the expanded dimensions of the Penguin Mailer (approx. 3" thick)

• Fit closely to minimize shifting and reduce dimensional weight

Coldkeepers can provide size-specific guidance depending on the model or size of Penguin Mailer you’re using.

No — the puncture point is intentional and engineered for that exact purpose. It’s a small, designated area where you apply your shipping label after puncturing, allowing for pressure relief and proper adhesion.

The puncture does not affect the insulating foam layer or structural integrity of the mailer. The high-performance 1.5” foam and metalized liner remain sealed and fully functional, preserving thermal protection throughout transit.

Coldkeepers designed this feature to ensure compliance with carrier labeling requirements without sacrificing insulation or product safety.

The Penguin is a compact, self-expanding insulated envelope designed for temperature-sensitive shipments. It arrives flat (just 0.5" thick) and expands to nearly 3" to form a thermal protective cocoon—no outer carton or void fill required.

• Load your product and PCM refrigerant into the mailer.

• Seal it using the attached tamper-resistant tape and zipper closure.

• Puncture and apply your shipping label.

The Penguin Mailer is ideal for:

• Pharmaceuticals

• Clinical specimens

• Chocolates and confections

• Frozen meats

• Temperature-sensitive foods or ingredients

• Space-saving: Ships flat and expands on demand.

• No outer carton: Reduces packaging waste and cost.

• No void fill needed: Conforms snugly to products.

• Durability: Features a strong 4.5 mil metalized liner and 1.5" insulated foam.

Yes. It includes:

• A pressure-sensitive, tamper-evident adhesive strip

• A leak-resistant zipper closure
These features provide both security and protection during transit.

Yes, the mailer is lightweight and compact, making it ideal for both domestic and international shipments, especially where freight cost and space are concerns.

• Ships flat → lower inbound freight

• No outer box → lower dimensional weight

• No void fill → faster packing process

• Less packaging waste → more efficient storage & disposal

Coldkeepers offers private labeling options. Contact our team to learn how your logo and messaging can appear directly on the mailer.