What are the best features to look for in bicycle covers to ensure they are waterproof?

When looking for a waterproof bicycle cover, the best features to consider are a durable and waterproof material such as polyester or nylon, sealed seams to prevent water leakage, and a secure fastening system like elastic hems or straps to keep the cover in place during windy conditions. Additionally, a UV-resistant coating can help protect the cover from sun damage and prolong its lifespan.