Think like a soda from McDonald’s or an iced coffee from Dunkin Donuts in the spring and summer. Even if you buy one and stay inside or quickly go inside where it’s air conditioned, the cup will always get “sweaty” and water condenses and gets everywhere.
This doesn’t happen during the cold seasons. Why does it occur even when you go where it’s climate controlled?
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It’s humidity. Humid air condenses on things that are cold like cups of cold drinks.
The “dewpoint” determines when that happens. On a hot, humid day, the dewpoint is in the 60s or 70s, so the glass doesn’t need to be that cold. The dewpoint is never more than the air temperature so in the winter it is harder to get condensation. Many indoor places need a humidifier to accompany their heating system as the air is so dry. You can see this with other objects. Golf clubs kept in my basement get wet when I take them outside to practice in my yard in a hot and humid day.
You can see this effect in the winter going the other way. When I am outside in the super cold, my eyeglasses get cold. Then when I go indoors the glasses will “fog up” immediately. The humidity inside is more than outside and the glasses from outside get super cold.
They’re extremely thin, so they draw the heat out of the moisture in the air faster than a glass or ceramic container. There’s always moisture in the air. If that moisture is cooled, it will condense. It’s not just about the temperature.
Difference in temperature causes condensation.
Warm air holds more moisture than cold air (relative humidty)
In winter, the drink and the air temperature are much closer, and the moisture in the air (relative humidity ) is typically lower so less condensation.
In summer the temperature difference is much higher and there’s typically more moisture in the air allowing condensation to form.
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