Every time we get in the car, on a wet day, we bring dampness into the car on our shoes and on our clothes and it’s this moisture that causes the inside of the car to mist up really badly. Getting rid of this moisture can be difficult as cars are so well sealed nowadays. I find opening the windows a little when the car is up to temperature helps but if you do short journeys and the car never gets a chance to dry out, the moisture catchers that you buy form the pound shop can help.