In some locations in the United States moisture can kill honey bee colonies over the winter months. This moisture is caused by the condensation of the water vapor as it rises from the cluster and cools at the interface between the warmer and colder air. This interface is usually at the inner cover in most hives. Bees can be killed by moisture if it builds on the inner cover and rains down onto the bees when clustered. The bees can tolerate the cold but not when they are wet. Many beekeepers will place an empty hive body above the inner cover for added protection against the cold. Some beekeepers will place different substrates within the space above the inner cover to soak up the humidity. I have heard some using compressed cardboard or even hay. There are many different materials to choose from and I use newspaper since it is fairly cheap. I crumble the newspaper into balls and place them in an empty hive body above the inner cover as shown below. You can see I put an open sheet over the top; it is easier to use as an indicator if the paper is wet when you pick this sheet up. In the picture above I used a formic acid shim instead of a hive body to place newspaper into. The newspaper can become saturated quick depending on the weather. It is important to remove and replace the newspaper once a week to prevent mold. If you are using screen bottom boards, you may need to change the newspaper more or less frequently.