Reviewed by Daniel M. · Last Updated September 23, 2026 · How we review
For most cold-climate hives, the best moisture board is a sheet of plain cellulose fiberboard, 1/2 to 3/4 inch thick, cut to fit your box. Homasote-type board works, as does the non-asphalt fiberboard the University of Minnesota Bee Lab specifies. Set it on the inner cover with the center hole left open, under the outer cover. The board to avoid is the asphalt-impregnated sheathing that most lumberyards stock under the same “fiberboard” name. Also skip anything that sags when wet or can’t absorb water at all. Below are the four tests a good board has to pass, how the common options compare, and why our Red River Valley winters make getting this right so important.
Key Takeaways
- A moisture board has to absorb water vapor from the cluster and release it outward. Rigid foam and plastic can’t do the first part.
- Choose plain cellulose fiberboard, never the asphalt-impregnated kind. The UMN Bee Lab warns against it specifically.
- The board should stay rigid when damp. Cellulose ceiling tiles can sag onto the frames once they soak up water.
- Fit matters. A board that’s too small lets moist air get around it and condense on the cold cover.
- A colony puts out a lot of water over winter. Every 10 lb of honey eaten releases roughly 6.5 lb of water, so pair the board with an upper entrance.
Table of Contents
How Much Water a Wintering Colony Makes
A wintering cluster heats itself by burning honey, and burning sugar produces water. Honey is roughly 80% sugars and 17% water. Each pound of sugar the bees burn releases about 0.6 lb of water, and the water already in the honey is added on top. That comes to about two-thirds of a pound of water vapor for every pound of honey eaten, or roughly 6.5 lb (about three quarts) for every 10 lb of stores.
That warm, moist air rises to the coldest surface above the cluster. In a hive, that’s the underside of the cover. Around Fargo, January averages a low of 1.2 °F under NOAA’s 1991–2020 normals (climate table). So the cover is far below the temperature at which that vapor condenses. The water forms droplets, and they drip straight back onto the bees. A moisture board is there to catch that vapor before it reaches the cold cover. For the full range of fixes beyond the board itself, see our guide to preventing hive moisture in winter.
The Four Tests of a Good Moisture Board
The University of Minnesota Bee Lab’s northern wintering method uses a moisture board over the inner cover, and its equipment notes say exactly what the board is for:
“It will absorb moisture from the inside of the hive and release it to the outside.”
Gary Reuter, University of Minnesota Bee Lab, “Wintering Tips”
From that purpose, four tests follow:
- It absorbs and releases water vapor. Cellulose fiberboard does both. Rigid foam, plastic and painted plywood don’t absorb anything. The UMN notes list plastic, styrofoam and kraft-faced insulation under things you should not use as the board.
- It holds its shape when damp. Homasote’s own specification for its 440 board rates water absorption at no more than 7% by volume after a two-hour soak (product data). That’s why it stays rigid through a winter of vapor. Beekeepers who’ve tried cellulose drop-ceiling tiles report they tend to go soft and sag.
- It has no coating. The UMN notes point out that fiberboard comes with or without impregnated asphalt, and to use only the kind without. Asphalt-treated sheathing is the default at many lumberyards, so check before you buy.
- It fits the box. Gaps at the edges let moist air go around the board and condense on the cover anyway. Buy for your box width (5, 8 or 10 frame), or cut a sheet to size.
Moisture Board Materials Compared
| Material | Absorbs vapor? | Stays rigid when damp? | Verdict |
|---|---|---|---|
| Homasote-type cellulose board (1/2–3/4 in) | Yes | Yes | The standard choice, and what many bee-supply moisture boards are made from. |
| Plain (non-asphalt) fiberboard sheathing, 3/4 in | Yes | Yes | The UMN Bee Lab’s specification. Check that the label says no asphalt. |
| Asphalt-impregnated fiberboard | Less well | Yes | Avoid. The UMN Bee Lab says not to use it. |
| Cellulose drop-ceiling tile | Yes | Often not | A stopgap only. It can sag onto the top bars. |
| Rigid foam board | No | Yes | This is insulation, not a moisture board. It keeps the ceiling warm but absorbs nothing. |
| Wood-shaving quilt box | Yes (loose fill) | n/a | A different, deeper design. See our quilt box vs moisture board comparison. |
| Newspaper stack, about 3/8 in | Yes | Fair | A one-winter stopgap that the UMN notes list as an option. |
On thermal value, a moisture board adds little insulation. Homasote rates its 440 board at R-1.2 for 1/2 inch and R-1.4 for 3/4 inch. Its job is to manage water, not to hold in heat. If you also want a warmer ceiling, that’s a separate layer and a separate decision. Our comparison of insulated hive tops vs plain telescoping covers covers it. Buying pre-cut is simplest. For example, Mann Lake’s 10-frame moisture board is a 1/2-inch board sized for 10-frame equipment. If you’d rather cut your own from a 4×8 sheet, our moisture board DIY guide walks through it.
Installing It in a Northern Hive
- Set it on the inner cover, under the outer cover, with the inner-cover hole left open so vapor can reach the board. If your board has a dark or painted face, that side goes up, away from the bees.
- Give the moisture a way out. The UMN Bee Lab method adds an upper entrance: a 1/2 to 1 inch hole in the top deep, with a matching hole cut in the winter wrap. Our comparison of upper vs lower entrances in winter explains the trade-offs.
- Wrap for wind, not to seal. A black wrap cuts wind and picks up a little solar heat, but it shouldn’t seal the board off from outside air. Our guide to hive wraps for cold climates compares the options.
- Install before the first hard freeze and check the board on a mild day in late winter. A board that’s damp but still firm is working. One that’s soaking wet, or has mold creeping up the underside, means the hive needs more upper ventilation.
A good board lasts several winters. Dry it out each spring, store it flat, and replace it when it starts to crumble or delaminate. For a full fall checklist, see winterizing beehives in northern states.
Frequently Asked Questions
What is the best material for a beehive moisture board?
Plain cellulose fiberboard, 1/2 to 3/4 inch thick. Homasote-type board is the common choice. Avoid asphalt-impregnated sheathing, foam, and ceiling tiles that sag when wet.
Does a moisture board go above or below the inner cover?
Usually above, sitting on the inner cover with its center hole open, under the outer cover. Some supplier kits skip the inner cover and set the board on a shim instead. Follow the kit’s directions if you use one.
Which side of a moisture board faces the bees?
The plain, unpainted side faces down toward the bees. If one face is dark or coated, it goes up.
Can I use foam insulation instead of a moisture board?
Foam and a moisture board do different jobs. Foam keeps the ceiling warmer so less vapor condenses there, but it absorbs nothing. If you use foam, make sure the hive still has upper ventilation.
How often should a moisture board be replaced?
A fiberboard moisture board typically lasts several winters. Dry it each spring and replace it once it crumbles, delaminates or smells musty.
The Bottom Line
The best moisture board is the plain one: uncoated cellulose fiberboard that fits your box, absorbs vapor, releases it outward, and stays rigid when damp. In a Northern Plains winter, pair it with an upper entrance and a wrap that doesn’t seal it in. It catches the water the cluster gives off before it can drip back on the bees.
