Gel air fresheners come in a small plastic canister or tin that fits perfectly into a car’s cup holder. Inside, a solid gel block slowly shrinks as it evaporates, releasing fragrance over time. The lid usually has adjustable vents, allowing you to control the intensity of the scent. Because the scent is suspended in a solid gel, there is no risk of liquid spilling. They are known for longevity, often lasting 30 to 60 days.