Storage

October 9, 2025

What is the humidity level to store cardboard boxes?

Discover the ideal humidity level to protect your boxes from mold and prevent them from deteriorating during storage.

Cardboard is a very practical material: lightweight, recyclable and economical, it is commonly used for packaging and storage. But it has a major drawback: it absorbs ambient humidity, which can weaken its structure and deteriorate its contents.

Why does humidity damage cardboard?

Cardboard is made from cellulose fibers, a naturally porous and hygroscopic material.
This means that it easily captures moisture in the air, much like a desiccant or a dehumidifier bag.

When the air becomes humid, water adsorbs onto the fibers, which swell and move away from each other.
 

Result:

  • the cardboard loses its rigidity,
  • it sags more easily under weight,
  • and it can develop mold if it stays in a humid environment.

This deterioration can also affect stored contents — documents, textiles, electronic parts, etc.

Recommended humidity level for storage

Studies show a direct correlation between relative humidity and the mechanical strength of cardboard.
According to Hanlon & Kelsey (1998), the stacking strength drops significantly when humidity increases:

  • 💧 At 50% relative humidity, the resistance is still around 80% of its maximum value.
  • ⚠️ Above 70%, it decreases rapidly.
  • 🚫 At 90%, it barely reaches 40% of its initial strength.

👉 In practice, it is therefore strongly recommended to store cardboard boxes at a humidity level of less than 70%, ideally around 50% for optimal preservation.

How do you maintain a good humidity level?

Here are some solutions to effectively control humidity in your storage spaces:

1. Properly insulate and ventilate the premises

Make sure your storage room is properly ventilated and insulated.
Natural ventilation or an electric dehumidification system can limit condensation and humid areas.

2. Raise the boxes

Avoid direct contact with the ground, which is a source of rising humidity.
Use pallets or an insulating pad to create a barrier between the ground and your boxes.

3. Use a humidity regulator

Desiccants like silica gel or anti-humidity bags can absorb excess water, but they have a limited lifespan and require regular replacement.

For a sustainable and maintenance free solution, innovative products like Air Sponge offer natural and continuous regulation of humidity, without energy and without waste.
An ideal alternative to protect your boxes over the long term.

In summary

The ideal humidity level for storing cardboard boxes is between 45% and 55%.
Below 70%, the cardboard structure remains stable and its mechanical strength is maintained.

To guarantee this stability, combine ventilation, insulation and humidity control using a suitable solution such as Air Sponge. You will thus extend the life of your packaging, while preserving its contents from humidity.

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