Unibond "moisture absorber". (presented as a room dehumidifier)

I noticed that ASDA (UK Walmart) was pushing these Unibond "moisture absorbers". The packaging is very misleading and tries to present these units as room dehumidifiers, giving condensation, mold and peeling wallpaper as examples of what they can "prevent". In reality they wont, because whereas a real dehumidifier will pull many litres of water out of the air in a damp room every day, this unit will only draw out about 700ml at best in a month or longer.
These units use cylinders of compressed hygroscopic chemical, (probably calcium chloride) to absorb moisture slowly, dissolving into liquid as they do so. You end up with the collection tray full of a saturated chemical solution which is not only quite corrosive to many metals, but will cause permanent damp stains if it gets spilled.
These things might be OK for keeping the humidity down in a cupboard with low air flow, but for room use they are nothing more than a placebo, and useless as an actual dehumidifier.

When the chemical block has fully dissolved in these units you have to pour the concentrated chemical solution down your drain and buy a new block. Compared to a real dehumidifier these units cost over ten times as much to extract a given quantity of water and do so very slowly.

In short, if you have a humidity issue then don't waste your money on this gimmick. Buy a proper compressor or desiccant-drum based dehumidifier that will actually do the job.

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