Stuffiness is either the quality of lacking good air flow or ventilation, like the stuffiness of an attic in the summer, or the characteristic of being narrow-minded and judgmental, like the stuffiness of your stern and proper Aunt Hilda.
There's the stuffiness of your parents' overheated car, and then there's the stuffiness of your nose when you have a cold—in the latter case, stuffiness means "having the quality of being stuffed up or congested." The personality trait of stuffiness applies to people who aren't open to change or to new ideas, but are stuck in a conventional way of thinking: "His stuffiness meant he could never really enjoy our rowdy parties."