The short version
- A passive moisture absorber uses no electricity at all, so once you have bought it there is nothing to run. A plug-in dehumidifier of the usual household size draws a couple of hundred watts.
- One tub pulls a few hundred millilitres of water a week in a cold, damp room. That suits a wardrobe, a caravan or one bad corner, not a whole wet house.
- Multipacks of disposable tubs are the cheapest way to cover several spots at once. Refill crystals only pay off if you already own a refillable trap.
- Ofgem’s price cap rises to £1,723 a year from 1 October 2026, so more homes will be heated less and aired less this winter, which is exactly what puts water on the glass.
Water on the inside of the windows is the first thing most people notice, and it tends to show up the same week the heating goes back on. Amazon UK’s Home & Kitchen best sellers already had two moisture absorbers inside the top 25 in late August, which is early even by British standards.
The reason is not much of a mystery. Ofgem has confirmed the price cap at £1,723 a year from 1 October, up £60, with the gas half doing most of the rising. Colder rooms and closed windows mean the moisture your household makes has nowhere to go, and cold glass is where it lands. The Energy Saving Trust’s own damp advice makes the same point: excess moisture plus poor ventilation is what causes condensation damp in the first place.
A £10 tub of crystals will not fix a house with a real damp problem, and nobody sensible should pretend otherwise. What it will do is take the edge off a specific spot. Below are six that are worth the money, and more importantly what each one is actually for.
As an Amazon Associate I earn from qualifying purchases. (paid link)
How we picked these
Every product here is a passive absorber. There is no fan and nothing to plug in. Most work on the same principle, which is a hygroscopic salt (usually calcium chloride) that pulls water out of the air and drips it into a reservoir you then pour down the sink. Silica gel works differently, holding moisture in a bead you dry out and reuse.
What we weighted:
- Format over brand. A hanging bag, a floor tub and a car sachet do different jobs, so the shortlist covers all of them rather than ranking six versions of the same tub.
- What it costs to keep going, which matters more than the sticker price when the thing is a consumable you rebuy every few weeks.
- Capacity claims that hold up. A 500ml tub means the reservoir holds 500ml, not that it removes 500ml a day, and anything sold on implausible extraction figures was left out.
- In stock and priced on Amazon.co.uk at the time of writing, with every ASIN checked against its own product page rather than the search listing.
For the health side we leaned on the UK government’s damp and mould guidance, which was produced with the UK Health Security Agency after the coroner’s report into the death of Awaab Ishak. It is written for landlords but the section on why moisture builds up applies to anyone.
At a glance
| Product | Best for | Format | Around |
|---|---|---|---|
| UniBond AERO 360 | Overall pick | Refillable tub, 450g tabs | £11 |
| ANSIO Disposable, 10 pack | Covering several rooms | Sealed 500ml tubs | £10 |
| ANSIO Wardrobe Hanging Bags, 12 pack | Wardrobes and cupboards | Hanging sachet | £10 |
| Kontrol Refill Crystals 2.5kg | Topping up a trap you own | Loose crystals | £16 |
| Homiu Car Dehumidifier Bags, 2 x 1kg | Cars, vans and caravans | Reusable silica gel | £14 |
| Wisedry Silica Gel, 2 x 500g | Stored clothes and boxes | Reusable silica gel | £20 |
The six worth a look
UniBond AERO 360 with one refill tab
Best overallThe one to buy if you are only buying one. The tab sits above the reservoir rather than in it, so the collected water cannot slosh back over the salt, and the shell is wide enough that it does not tip if a cat walks into it. Refills are sold everywhere, including supermarkets, which is worth more than it sounds when you need one in November. In a cold back bedroom it fills the reservoir in roughly six to eight weeks.
The catch: the refills are the business model. At about £2 to £2.50 a tab you will spend more on tabs in a year than you did on the unit, and the lavender version smells strongly enough that some people move it out of the bedroom.
Device plus one 450g tab · around £11
Check price on Amazon →ANSIO Disposable Moisture Absorber, 10 pack
Best for covering several roomsTen sealed 500ml tubs for about a pound each, which is the cheapest honest way to put an absorber in every room that needs one. You peel the lid, sit it on a windowsill and bin it when the crystals have collapsed into liquid. No refills to source, no lid to lose. This is the format that keeps turning up in the Amazon UK best sellers, and the price is why.
The catch: you are throwing away a plastic tub every few weeks, which adds up over a winter. The tubs are also light and easy to knock over, and the liquid inside is a salt solution that will mark a painted sill if you spill it.
10 x 500ml sealed tubs · around £10
Check price on Amazon →ANSIO Wardrobe Hanging Bags, 12 pack
Best for wardrobes and cupboardsThe musty smell in a wardrobe on an outside wall is the single most common thing people buy these for. A hanging bag solves it properly because it sits in the air the clothes are in, rather than on the floor below them, and there is no reservoir to knock over among your shoes. Twelve bags will see a family through a winter with spares for the understairs cupboard.
The catch: the collected water stays in the bag, so it gets heavy and the hook can pull off a flimsy rail. Check it every few weeks, because a split bag in a wardrobe is a considerably worse problem than the damp was.
12 hanging sachets · around £10
Check price on Amazon →Kontrol Refill Damp Trap Crystals, 2.5kg
Best for a trap you already ownA big tub of loose crystals for anyone who already has a refillable trap sitting empty in the garage. Scent free, so it will not fight with whatever else is in the room, and 2.5kg goes a long way when you are filling a trap two or three hundred grams at a time. Handy too if you use a large open container in a cellar or garage where a branded tab would be swallowed whole.
The catch: per gram it is dearer than the disposable multipacks, so this is not a money-saving move unless you value keeping the trap out of the bin. Loose crystals are also messier to handle and need to go somewhere pets and small children cannot reach.
2.5kg loose crystals, scent free · around £16
Check price on Amazon →Homiu Car Dehumidifier Bags, 2 x 1kg
Best for cars and caravansFoggy windscreens in the morning are a moisture problem, not a heater problem. A kilo bag of silica gel on the dashboard cuts down the demisting time on a cold start, and because these recharge in a microwave or a low oven you are not buying replacements every month. The anti-slip pads matter more than they sound, because a loose kilo bag will end up in the footwell on the first roundabout.
The catch: recharging is a faff. It takes several minutes in the microwave and the bag comes out hot, and if you leave it too long you can scorch the fabric. Two bags is also the minimum for a family car, so you are recharging both.
2 x 1kg reusable silica gel, with pads · around £14
Check price on Amazon →Wisedry Reusable Silica Gel, 2 x 500g
Best reusable optionColour indicating beads that turn from orange to green as they fill up, which removes the guesswork entirely. Sized for vacuum bags, storage boxes, a camera bag or the winter duvet going up into the loft, and it reactivates in the microwave in a few minutes. Buy this instead of calcium chloride anywhere a leaked salt solution would ruin what you are protecting.
The catch: silica gel holds far less water by weight than calcium chloride, so it is the wrong tool for a genuinely wet room. It is also the dearest thing on this list, and you only get your money back if you actually bother to recharge it.
2 x 500g, colour indicating · around £20
Check price on Amazon →Frequently asked questions
Do moisture absorbers actually work?
Yes, within limits. Calcium chloride genuinely pulls water out of the air and you can watch the reservoir fill. The limit is scale. A tub might collect half a litre over several weeks, while a household of four can put something like ten litres of moisture into the air in the same period through washing, cooking and breathing. Treat one as a fix for a cupboard, not for a house.
Is a moisture absorber better than an electric dehumidifier?
They are not really competing. An electric dehumidifier can shift several litres a day and dry laundry, but it needs a socket and draws a couple of hundred watts while it runs. An absorber costs a few pounds, works in a wardrobe or an unpowered caravan, and shifts a tiny fraction of that. If your windows are running with water every morning across the whole house, you want the plug-in one.
Where should I put one?
Nearest the cold surface and out of a draught. Windowsills, the floor of a wardrobe on an external wall, the corner of a bathroom without an extractor, and inside a caravan or boat over winter. Putting one in the middle of a room with the door open achieves very little.
Are the crystals safe around children and pets?
Calcium chloride is an irritant. It is not the deadly poison some listings imply, but it will burn skin and eyes on contact and the collected liquid should not be drunk. Keep tubs and loose crystals out of reach, mop spills straight away, and choose the hanging bag or silica gel formats if you have a curious toddler or a cat that investigates everything.
How often do they need changing?
In a cold, damp UK room over winter, expect four to eight weeks from a 450g tab or a 500ml tub. In a dry, heated room it can be months. You will know because the crystals stop looking like crystals and the reservoir stops filling.
Will one stop mould?
Not on its own. Mould needs sustained high humidity, and the government’s damp and mould guidance is clear that ventilation and heating are what actually fix the underlying cause. An absorber helps in a confined space where you cannot ventilate. If there is black mould spreading on a wall, that is a building problem and worth reporting to your landlord or getting looked at.
Sources
- Damp and mould: understanding and addressing the health risks for rented housing providers, Ministry of Housing, Communities and Local Government with DHSC and UKHSA
- How to get rid of damp, Energy Saving Trust
- Energy price cap and standing charges explained, Ofgem
Our moisture absorber pick also features in the UK Student Kit Index, where we price the full 20-item student room kit every year.