If you read the tag on the cover of your boat, ATV or motorcycle, you will probably see some terms such as "waterproof", "water-resistant" or "water-repellent". They seem like having the same meaning; however, in fact there is a difference between a waterproof cover and a water-resistant cover.
What's the difference between all these terms? Here's how Merriam-Webster online defines them:
Water-resistant and water-repellent essentially mean the same thing. A water-resistant cover is specially treated to resist water, but in heavy rains, water may still get through. Water-resistant covers only prevent water from getting through the cover up to a certain point. Your boat or ATV may still get wet in a downpour.
A waterproof cover, on the other hand, is designed to keep out heavy rains. The seams are taped or sealed to keep water from entering through the tiny needle holes in the fabric seams. Although a waterproof cover sounds like the better of the two types of covers, it does have its weaknesses.
First, the time and effort required to waterproof a cover adds to the overall cost. If you choose a waterproof cover over a water-resistant one, be prepared to shell out the extra change.
Second, because of the water-tight nature of a waterproof cover, any condensation that builds up under the cover stays under the cover and can potentially cause moisture damage to your boat or vehicle. That's why some manufacturers design their waterproof covers with vents to allow the condensation to evaporate and to prevent moisture damage. A breathable, waterproof cover will fully protect your boat, ATV, or other powersports vehicle from exterior and interior moisture.
Also keep in mind that one boat or motorcycle cover may be more waterproof than another, depending on the quality of the fabric and its resistance to water pressure. According to Wikipedia, "water resistance is measured by the amount of water, in millimeters, which can be suspended above the fabric before water seeps through." So the more water pressure that a piece of fabric cover can withstand, the more likely it will be to keep your boat or motorcycle dry in heavy rain or snow.