the three depths of standardized Langstroth supers. Frames are inexpensively mass-produced. Most beekeepers find it uneconomical to make frames themselves. The woodwork is too intricate and repetitive without specialized tooling. Since the frame might touch both honey and bees, frames are usually made from inexpensive, nontoxic softwoods such as eastern pine. Plastic frames are also available. When new frames are installed, they are filled with "foundation," artificial comb made of recycled natural beeswax or plastic. Beeswax foundation usually requires support from metal wires threaded through a frame. Foundation is widely used because bees make wax from carbohydrates that would otherwise be used to make honey. Some references say that as much as of honey is sacrificed for of wax. The use of recycled beeswax concerns beekeepers because it can transmit diseases, such as American Foulbrood. Some beekeepers, such as Christy Hemenway, have said that they believe that insecticides can be concentrated in the recycled wax, harming bees' health. The frames in the Langstroth patent were not designed to use foundation. The top bars of the patent Langstroth frames were "comb guides," 60-degree triangular prisms of wood pointing downwards. These encourage the bees to construct new comb along the edge of the prism, within the frames. Some beekeepers today practice foundationless beekeeping. Bottom board and entrance reducer The bottom board is almost always exterior-grade plywood, to resist water damage. It keeps dampness and some pests out of the lower brood chamber. It rests on wooden rails, which in turn rest on the ground. Some beekeepers place the rails on bricks or sand to reduce water and termite damage. Langstroth's patent shows a wooden hive stool that lifts the hive several feet from the ground, to a convenient working height for a beekeeper. A white plastic sheet is sometimes coated with a slightly sticky substance, and slid over the bottom board to trap and count fallen varroa mites, a bee parasite that can infest hives. The entrance reducer is a square bar of wood to help the bees manage air circulation. Bees naturally manage their hive's temperature with fanning, clustering and shivering. The reducer helps bees stay warm in winter, and fan less energetically in summer. It may drop into notches in the wooden rails or the bottom board. It has two different-sizes of bee entrance notches cut into it, on different sides of the bar. In winter, the reducer is turned