For most of the history of the desktop humidor, the humidifier inside it was a block of green foam in a plastic housing. It was cheap, it was simple, and it came with the box. Many humidors still ship with one, and many collectors still use it, out of habit more than conviction. It is worth being precise about what it does and does not do, because the difference between foam and a two-way pack is not a matter of degree. It is a matter of direction.
How the foam humidifier works
The principle could not be simpler. A block of open-cell foam is soaked in distilled water or a propylene glycol solution and clipped to the underside of the lid. Water evaporates from the foam into the air of the box, and the cedar and the cigars take up what they need. As long as the foam holds water, humidity rises toward whatever the room and the box will allow. When it dries out, the owner refills it and the cycle begins again.
The propylene glycol variant is a partial answer to the obvious problem. Glycol is hygroscopic and, in the right mixture, slows evaporation so that the block tends to plateau near 70 per cent rather than climbing without limit. It is a real improvement over plain water, but it is a brake rather than a regulator. It slows the addition of moisture; it does not reverse it.
One direction only
That is the structural flaw, and no amount of careful use removes it. A foam humidifier can only ever add humidity. If the air in the box is too dry, it helps. If the air in the box is too wet, it does nothing at all, or continues to make matters worse. It has no means of taking moisture back.
In a heated Canadian house in January, when the room air may sit near 25 per cent relative humidity, this hardly matters. The box is losing moisture to the room through every imperfection in the seal, and the foam is working against a steady outward flow. It may struggle to keep up, but it is at least pushing in the right direction.
The trouble arrives with the humid months. In a Toronto or Montreal summer, indoor air without air conditioning can carry 65 or 70 per cent relative humidity on its own. The cedar absorbs from the room. The cigars absorb from the room. And the foam, charged and dutiful, continues to evaporate into a box that already has more water than it needs. The interior climbs past 72, past 75, and stays there, because nothing in the system is designed to bring it down. The owner, having done everything the instructions said, opens the lid to find soft, spongy cigars and a hygrometer reading they cannot explain.
What follows
Sustained humidity above roughly 75 per cent has two consequences, and neither is cosmetic.
The first is mould. Tobacco carries spores as a matter of course, and they remain dormant as long as the environment stays within reason. Give them warmth and wet air for a few weeks and they grow, most visibly as blue-green or white fuzz at the foot or along the seam of the wrapper. Mould is not the same as plume, and it does not wipe off harmlessly. A cigar with mould on the wrapper generally has it in the filler as well, and the box it lived in needs to be emptied, wiped and re-stabilised before it can be trusted again.
The second is the smoke itself. An over-humidified cigar draws poorly because the filler has swollen and closed the channels through it. It burns unevenly, tunnels, and needs constant relighting. The flavour turns sour and flat, because the combustion temperature is wrong. Many cigars written off as badly rolled were, in fact, simply too wet on the day they were smoked. The damage is reversible in a stable environment, but it takes weeks, and the smoker rarely waits.
The two-way alternative
A Boveda pack works on a different principle. Inside is a saturated salt solution — salt and water in a proportion that does not change — behind a membrane that lets water vapour through but holds the liquid in. Above a saturated solution of a given salt, the air settles at a fixed relative humidity, and the pack simply reproduces that equilibrium inside the box.
The consequence is that the exchange runs in both directions. When the box is drier than the pack's rating, vapour leaves the pack and the humidity rises. When the box is wetter than the rating, vapour enters the pack and the humidity falls. The pack does not decide when to switch; the physics decides for it, continuously and without any intervention from the owner. A 69 per cent pack in a humid August pulls moisture out of the box exactly as readily as it pushes moisture in during a dry February.
This also means a pack cannot overshoot its own rating. However many packs are placed in a box, the interior cannot be pushed above the number printed on them. The failure mode that foam invites — an unbounded climb in wet weather — does not exist.
A fair comparison
It would be unfair to pretend foam has no virtues. It is inexpensive. It is reusable indefinitely. In a cool, dry climate, in a well-sealed box that is checked weekly and refilled with care, it can keep cigars acceptably for years, and many collectors have done exactly that. Its defenders are not wrong that it can work.
The comparison is better framed as a matter of what each device asks of its owner.
- Foam asks for a refill schedule, a measured solution, a reliable hygrometer that is read often, and a plan for what to do when summer arrives. It works when the owner works.
- A two-way pack asks to be placed in the box and pressed between finger and thumb now and then to check that it is still soft. It is replaced when it goes rigid, roughly every two to four months depending on the seal. It works whether or not the owner is paying attention.
There is also a question of what happens on the bad day. A foam block left too long simply dries out and the box drifts down slowly, which is recoverable. A foam block topped up before a humid spell pushes the box past 75 and holds it there, which may not be. A pack cannot produce that second outcome. The worst it can do is finish, at which point the box drifts gently toward the room, exactly as it would with dry foam.
Making the change
Switching is straightforward, with two cautions.
Take the foam out entirely. Running a pack alongside a charged foam block gives the pack a second source of moisture to fight against, and it will spend its life absorbing what the foam releases. The whole point of two-way control is lost if a one-way device is still pumping into the same space. Remove the block, and remove the housing too if it is not needed; an empty plastic case does nothing but take up room.
Choose one RH level and stay with it. The common choices for premium cigars are 65, 69 and 72 per cent. Do not mix levels in the same humidor; packs of different ratings pull against one another and both are exhausted quickly. As a rough guide, one size 60 pack serves about twenty-five cigars, and a box with a soft seal wants more than that. Packs are safe in direct contact with cigars and can rest on top of them or against a side wall, wherever air moves freely.
Give the box a few days to settle after the change. If it has been running high on foam through a summer, the cedar will be carrying excess moisture, and the packs will spend their first week or two drawing it out. The hygrometer will fall gradually rather than at once. That is the two-way exchange doing precisely what it exists to do.
El Laguito Cigars carries Boveda as an authorized retailer, in the RH levels and sizes a home humidor calls for. If a green foam block is still clipped inside your lid, the most useful thing you can do for your cigars this season is to take it out.