Where suction is lost
A vacuum that has lost its suction almost always has a blocked filter, not a failing motor. We cover cartridge and foam filters by class, fleece bags against paper, washable filters and how many washes they really survive — plus the wet-vacuuming rule that a cartridge filter must come out before water goes in.
The consumable that decides whether your vacuum keeps its suction through a whole job.
Same fleece construction as the KFI 487, in the size the smaller WD vacuums take.
The component that decides whether wet pick-up needs a filter change — and it is a consumable.
A longer-lasting element for dusty work — not a licence to vacuum plaster with an L-class machine.
A washable filter is rinsed and dried for twenty-four hours; a paper one is bought again. Stated washability decides the cost over five years.
Kärcher KFI 357 Fleece Filter Bags
A filter of near-enough diameter leaves a gap that all the dust goes through. The stated diameter and height matter more than the filter's brand.
Kärcher KFI 4440 Renovation Flat Pleated Filter
As soon as suction drops while the drum is not full. On fine dust that can happen within a single session; on coarse debris, after several months.
Only if it is marked washable. A wet paper filter deforms and loses all sealing, even once dry. Washing it amounts to throwing it away.
It is the minimum level for wood, plaster and concrete dust. Below it, fine particles pass through, stay airborne in the room and are breathed long afterwards.
The dust filter, yes, always, and fit the foam filter if one is supplied. It is the most frequent and most expensive mistake on these machines.
Often yes for the geometry, less often for the real filtration class, which is rarely verifiable. Where the dust is dangerous, the original remains the safe choice.
A holed filter, a badly seated one, or an insufficient class for what is being picked up. A badly seated lid gasket produces exactly the same symptom.
No, it protects it. The filter stays in place and lasts far longer when a bag holds back the bulk upstream.
Yes, for a simple reason: a washed filter dries for twenty-four hours, and without a second one the machine stands idle. Twin packs cost less than two separate purchases.
The filter decides what the machine throws back into the room, and falling suction comes from it nine times out of ten. Choose the class according to what you pick up, take it out before any wet pick-up, and treat it as the consumable it is.
A figure has to be published by four machines in five to earn its column. Below that, we would be comparing empty cells.
| Model | Price | Amazon reference |
|---|---|---|
| Kärcher KFI 357 Fleece Filter Bags | 15 $ | B09N1BPYTG |
| Kärcher KFI 487 Fleece Filter Bags | 16 $ | B00HVSORU8 |
| Kärcher KFI 4410 Flat Pleated Filter | 23 $ | B00HVSOS2A |
| Kärcher KFI 4440 Renovation Flat Pleated Filter | 25 $ | B0CT822H4K |
Specifications: manufacturer sheets for cleaning machines and the matching Amazon product pages. Prices and availability: Keepa. Every figure in this table names its source.
Most recent revision in this category: August 15, 2026.
Prices quoted in these summaries are dated readings. The live price is shown next to each product.