The purpose of the quilt box
It's literally everywhere (except on this website) that you might read about Warré hives; "the quilt box prevents the build-up of condensation within the hive by absorbing moisture from the air that enters the hive at the bottom, and then rises and passes through the quilt box before it exits the hive". Indeed, this is the way its function is described in Warré's book, Beekeeping for All, and it seems reasonable enough on its surface. But to use the word "absorbing" when describing the quilt's function is inaccurate at best, and at worst it's misleading and confusing. The purpose of the quilt box is to insulate the top of the hive during cold weather, which helps the bees stay warm and, more importantly, prevents water vapor from condensing into water droplets at the top of the hive and then dripping onto the bee cluster. The truth is...most materials can only actually absorb liquid water; like the wetting of a sponge. The sponge absorbs water, gets wet, and then dries out through the process of evaporation. When water vapor is mitigated from the hive, it happens through a process called diffusion. This diffusion is the action of water molecules actually passing right through solid or semi-solid objects (propolis, canvas, sawdust and wood). The action of measurable amounts of air moving through the hive actually has very little to do with this process, which is the whole point. It is the rising of heat and moisture; the transferring of heat to an area with less heat and the diffusion of moisture to an area that is drier. The last part of quilt science that I'm going to address here is moisture permeance, which is an object's resistance to (or lack thereof) this diffusion. This measurement is rated in perms. For example, glass and tin foil have very low perm ratings (little or no moisture can diffuse through them), while cotton cloth has an almost infinitely high perm rating. Anything with a perm rating higher than 10 is considered to be very permeable. I want to stress the importance of permeance because people frequently ask about heavy propolis on the screen (below the quilt box) and/or the fact that there are no ventilation holes cut into the side of the quilt box. They worry that a lack of air-flow will prevent moisture from escaping the hive. It won't. Everything that the quilt and roof consist of have perm ratings that are very high; all well over 100. There are other principles that help to further explain quilt functionality; warm air can hold more moisture than cold air, relative humidity, evapriation, dew point, etc., but I feel that this is the best short scientific explanation I can give you. The key things to remember about the function of the quilt box are these:
- The quilt box provides insulation for the hive (thus, the name).
- During the winter months, this insulation keeps the bees warmer and prevents condensation from forming above them and then dripping down on them. In winter, wet bees are dead bees.
- Moisture is mitigated from the hive through the quilt; it is not absorbed by it. It is possible that during certain conditions (cold temps and high outdoor humidity), moisture may condense inside the quilt box (near the top of or above the sawdust). But because of the permeability of the materials, this moisture will dissipate very quickly once conditions outside become drier.
- Condensation will not occur during the summer months even if all of the insulation is removed from the quilt. In fact, the insulation can cause the hive to overheat during the summer months an should be removed or at least pushed into the corners so that more heat can escape from the hive during hot weather. Basically, reduce the R-value (amount of insulation) in the quilt when nighttime temperatures are no longer dropping below 50F. If you have a problem with pests (ants, earwigs, etc.) hanging around in the quilt box during the summer months, just remove the sawdust altogether.
The last thing I want to talk about is the quilt filler material. Because the quilt's primary purpose is to insulate, material that provides the highest R-value is the best. Fine sawdust provides the best R-value if it is stirred regularly, but it settles quickly and then the R-value is reduced. Shredded wood or wood chips do not provide good R-value because they are too coarse. What we provide for filler is the sawdust that comes from our wood planer. It's coarse enough to not settle and get cakey, but fine enough to provide good R-value. We've found that this material gives the best overall performance.