Humidity: The Bane of Outdoor Electronics

Condensation inside an outdoor enclosure feels like weather on the inside. Warm, moisture-laden air creeps in during the day, the sun goes down, the box cools below dew-point, and—boom—droplets form on your circuit board.

The gut reaction is to hermetically seal everything. That works—until pressure swings balloon your gaskets or you trap a little moisture during assembly and can’t get it back out. Heating the box is another trick, but 24/7 watt-burn doesn’t fly on low-power deployments.

Even perfect seals fatigue. Daily thermal cycles tug at rubber gaskets until hairline gaps appear—now your “sealed” box is just a damp cave waiting for the next cold snap.

Let It Breathe—But Don’t Let It Drown

Enter the pressure-equalizing breather vent. The ePTFE membrane acts like Gore-Tex—air diffuses, liquid water stays out. Your enclosure ex- hales and inhales slowly, sparing the gasket and slashing condensation risk.

Add a humidity-control sheet (HCS) such as FiberSource’s Active-S line. Unlike plain silica gel, these polymer sheets absorb and release moisture, stabilizing RH around 40-60 % for years.

The winning recipe:
• IP-rated enclosure and cable glands
• PTFE breather vent up high
• One or two Active-S sheets inside (mount on sidewall, not the bottom)
• Optional low-watt heater for deep-freeze nights

Follow that playbook and your COTS electronics can survive 5-10 years in the wild without growing a rainforest on the PCB. Moisture may be the bane of outdoor electronics, but with smart breathing and a silent humidity butler inside, it doesn’t stand a chance.