Breathability is an important feature to look for when purchasing an RV cover. Many people ask us if our covers are waterproof. A cover that is waterproof will not allow any water to pass through it. This is good for repelling rain, but water can evaporate off the ground and then moisture can become trapped under the cover. This can cause mold and mildew to grow on your cover and RV. That is why you want a cover that is not completely waterproof, but one that is water repellent and breathable. A water repellent cover will still repel rain, but because it is breathable, it will allow the moisture that gets under the cover to evaporate as well. This helps to prevent mold and mildew. All the covers sold at RVCoversDirect are water repellent and breathable.