Five methods are in common use on carpet: hot water extraction, cold water extraction (more accurately, normal-temperature water extraction), encapsulation, bonnet cleaning and dry compound cleaning. Only the two extraction methods clean the full depth of the pile. The other three clean the top of it, quickly, so that a floor can stay in use. That single distinction explains almost every disagreement people have about carpet cleaning, and it is the one worth understanding before you book anything.
What follows is each method on its own terms: how it works, what it genuinely does well, and where it stops. Our own work is water extraction at normal temperature, and the reasons for that are set out below alongside everything else rather than in place of it.
The distinction that separates every method: depth
Soil sits in a carpet in three layers, and every method is really a claim about how many of them it reaches.
- Surface litter. Hair, crumbs, loose dust and the grit walked in this week. It sits on top of the pile and around the tips of the fibre. A vacuum removes most of it.
- Mid-pile soil. Fine particulate and body oils that have worked down between the fibres, plus the film left behind by spills and by any detergent that was never rinsed out. This is what makes traffic lanes look darker than the rest of the room.
- Base of the pile and the backing. Compacted grit, sand, skin cells, dust mite waste and, in pet households, urine salts in the backing. This is the layer that abrades the fibre with every footstep, and the layer responsible for odour that returns whenever the humidity rises.
Surface methods reach the first layer and part of the second. Extraction is the only approach that flushes the third, because the third layer only leaves the carpet suspended in water that is then pulled back out. Everything else in this comparison follows from that.
Hot water extraction
How it works. A cleaning pre-spray is applied to the pile and left to dwell, the pile is agitated so the chemistry reaches the fibre properly, and then a wand injects heated water under pressure and immediately vacuums it back out along with the suspended soil. It is the method the industry regards as the primary deep clean for textile floor coverings, and it is what most people mean when they say steam cleaning, although no steam is involved.
What it does well. It reaches the base of the pile. Heat speeds up the chemical action of the pre-spray and softens oily soil, so on a heavily greased synthetic carpet it does buy something real.
Where it costs you. Heat is indiscriminate. It opens the scales on wool and can felt and shrink it permanently, it makes dyes more soluble and therefore more likely to migrate, it sets protein stains such as blood, milk and egg by coagulating them into the fibre, and on older carpet it can weaken the adhesive and the jute secondary backing. None of that is reversible.
Dry time. 2 to 6 hours, decided by how much moisture is left in the pile rather than by the temperature of the water.
Cold water extraction (normal-temperature water)
How it works. Mechanically identical to the method above, with one variable changed. The pre-spray is applied and left to dwell, the pile is agitated, and then the wand flushes the pile with clean water at normal temperature and recovers it. The water in the wand is a rinse: all of the chemistry sits in the pre-spray, which is deliberate, because chemistry added at the extraction stage is exactly what stays behind in the pile.
What it does well. It reaches the same depth as the heated version, and it does it without any of the heat risks. Wool, wool blends, silk pile, viscose blends and unstable dyes all tolerate it. What heat would have contributed is made up with dwell time, correct chemistry for the fibre and proper agitation, which are three levers that carry no risk of shrinking or bleeding anything.
Where it costs you. On a very heavily greased synthetic carpet, an industrial situation rather than a domestic one, heat would get there faster. The trade is more dwell time and a stronger pre-spray instead.
Dry time. 2 to 6 hours. This is the method we use, and the reasoning behind that choice is set out in full in cold water extraction versus hot water extraction.
Encapsulation
How it works. A polymer solution is misted onto the carpet and brushed through the pile, then left to dry. As it dries it crystallises around each particle of soil into a brittle, non-sticky crystal that releases from the fibre, and those crystals are vacuumed away, either at the end of the visit or at the next routine vacuum.
What it does well. Very little water is used, so the carpet is walkable in roughly 20 to 60 minutes. On commercial synthetic carpet in corridors, open-plan offices and retail floors that never really close, encapsulation keeps appearance levels up at low cost and with almost no downtime. As a frequent maintenance clean it is genuinely good at its job.
Where it costs you. It is a surface-to-mid method. It does not flush the base of the pile, it does little for heavy soiling or set stains, and it does nothing for pet urine, which needs moisture and enzyme action to break the uric acid crystals down. It also suits synthetics far better than wool.
Dry time. 20 to 60 minutes. There is more detail in what encapsulation carpet cleaning is.
Products. For encapsulation cleaners we recommend Environ HP and Kärcher's RM range. Both are formulated for what the method actually has to do, which is leave a polymer that dries to a brittle, non-sticky crystal around the soil so it releases from the fibre and vacuums away. That is the whole trick, and it is where a general-purpose detergent used in the same machine fails: it dries tacky instead, holds soil at the surface and pulls more back to the same traffic lane within weeks.
Bonnet cleaning
How it works. A light solution is misted on and a rotary machine fitted with a round absorbent pad, the bonnet, is spun across the carpet. The pad agitates the top of the pile and wipes the loosened soil into itself, much like cleaning a surface with a damp cloth.
What it does well. It is fast, cheap and dries in about an hour, which is why hotels and offices use it to top up the look of traffic lanes between deeper cleans.
Where it costs you. It reaches the top of the pile only. Two further risks matter. Solution that is misted on and never rinsed out leaves residue in the pile, and residue attracts soil, so an over-applied bonnet clean can leave a carpet re-soiling faster than it did before. And the rotary action can fray, fuzz and distort pile over time, especially cut pile, which is wear that cannot be undone. It is not suitable for wool.
Dry time. Under an hour. More in what bonnet cleaning is and when it is used.
Dry compound cleaning
How it works. A slightly moist absorbent compound, usually a carrier material holding a small amount of solvent and detergent, is spread over the carpet and brushed into the pile with a counter-rotating machine. The compound absorbs soil as it works through the fibre, and the whole lot is then vacuumed out.
What it does well. It is the driest method of the five. The carpet is usable immediately, and it is genuinely useful where water simply cannot be used: over a floor that must not get damp, in a room that cannot be closed for an afternoon, or on a fibre that reacts badly to moisture.
Where it costs you. It cleans the upper pile, not the base. Because the compound is vacuumed rather than flushed out, some of it remains in the pile, and repeated dry compound cleaning without any extraction builds that residue up over the years. It does nothing for urine or for deep odour.
Dry time. Effectively none.
At a glance
- Hot water extraction. Deepest clean, real heat risk on wool, silk, dyes and older backings. Dry in 2 to 6 hours.
- Cold water extraction. The same depth without the heat risk, using dwell time and agitation in place of temperature. Dry in 2 to 6 hours.
- Encapsulation. Fast commercial maintenance on synthetic carpet, surface to mid depth. Dry in 20 to 60 minutes.
- Bonnet. Fastest appearance refresh, top of pile only, pile wear risk if overused. Dry in under an hour.
- Dry compound. No downtime at all, upper pile only, leaves compound behind. No drying time.
Which method suits which situation
- A home, once or twice a year. Water extraction. Household soil is deeper and more varied than office soil, it includes food, oils and pet accidents, and a home can afford an afternoon of drying. Any surface method here is spending money on appearance without removing the grit that is wearing the carpet out.
- Wool or a wool blend. Water extraction at normal temperature, with pH-appropriate chemistry. Rotary pads and alkaline maintenance chemistry are both poor choices on wool, and heat is the worst of them. See why wool needs wool-safe cleaning.
- Pet urine anywhere in the picture. Extraction, with enzyme treatment. This is not a preference. Urine crystallises into salts that only break down when moisture and an enzyme reach them, and every low-moisture method leaves them where they are.
- A busy office floor between deep cleans. Encapsulation on a regular cycle, with extraction periodically. The two are complementary, not competing.
- A hotel corridor that has to look presentable tonight. Bonnet, used sparingly and with a light hand on the solution.
- A room that genuinely cannot be wet. Dry compound, understanding that it is buying time rather than cleaning the carpet through.
- A carpet that is re-soiling within weeks of its last clean. Extraction with a thorough rinse. The likely cause is detergent residue left in the pile by an earlier clean, and only flushing removes it. See why carpets get dirty again quickly.
Rugs are a different question
None of the five methods above is how a rug should be cleaned. A rug is a free-standing textile with a foundation that holds soil in a way fitted carpet does not, and it can be immersed, flushed and dried flat under controlled conditions, which a fitted carpet can never be. Synthetic rugs go through a rug-washing machine, because agitation and volume of water give a stable synthetic pile the deepest clean it can take. Wool, silk, viscose, cotton, kilim and hand-knotted pieces are washed by hand.
The one place these methods reappear in rug care is on fibres that must not be wetted at all, which is a genuinely short list and is covered in dry cleaning a rug, and which fibres actually need it. Our rug cleaning service page sets out the full method.
The questions worth asking whoever you book
You do not need to know the methods by name to get a straight answer. Three questions do the work:
- What are you doing about the soil at the base of the pile? If the answer does not involve flushing the pile and recovering the water, it is a maintenance clean, which may be exactly what you want, but you should know that is what you are buying.
- How are you identifying the fibre, and what changes if it is wool? The chemistry and the temperature both have to change. If nothing changes, the fibre was not identified.
- What rinses the cleaning chemistry back out? Detergent left in a pile attracts soil and keeps attracting it. A clean that ends without a rinse is a clean that re-soils.
Our full sequence is set out on the 7-step process page, and rates for both carpet and rugs are published on the pricing page.
Common questions
Which carpet cleaning method is best?
Water extraction, for any clean where the point is to actually remove soil rather than to refresh appearance. It is the only method that flushes the base of the pile and the backing, and it is the only one that addresses pet urine, allergens and set stains. Encapsulation, bonnet and dry compound cleaning are maintenance methods: they keep a floor looking acceptable between deep cleans with minimal downtime, which is a real job, just not the same job.
What is the difference between encapsulation and hot water extraction?
Depth and water. Encapsulation crystallises the soil it can reach into brittle particles that are then vacuumed away, using very little moisture, so the carpet dries in 20 to 60 minutes but the base of the pile is untouched. Extraction flushes the whole pile with water and vacuums that water back out, removing embedded grit, allergens and dissolved stains, and dries in 2 to 6 hours. Encapsulation is maintenance; extraction is the deep clean.
Is dry carpet cleaning as good as wet cleaning?
Not for depth. Dry compound cleaning works the upper pile and leaves the compacted grit, urine salts and allergens at the base of the pile in place, and some of the compound stays behind in the fibre. It is the right choice when a floor genuinely cannot be wetted or cannot be taken out of use, and the wrong choice when the carpet is actually dirty. The honest framing is that it buys appearance and time, not a clean carpet.
Is bonnet cleaning bad for carpet?
Used occasionally on commercial synthetic carpet it is fine for what it is. Used often, the spinning pad frays, fuzzes and distorts pile, particularly cut pile, and that wear is permanent. The second risk is residue: bonnet solution is misted on and never rinsed out, so an over-applied clean leaves detergent in the pile that attracts soil and speeds re-soiling. It is not suitable for wool.
Which method is best for pet urine?
Water extraction with enzyme treatment, and nothing else comes close. Urine dries into uric acid salts that bond to the fibre and the backing and are not water-soluble on their own. They need moisture to reactivate, an enzyme with enough dwell time to break them down, and then extraction to pull the broken-down compounds out. Encapsulation, bonnet and dry compound cleaning all leave the source of the odour exactly where it is, which is why the smell returns on the first humid day.
Does the cleaning method change the drying time?
Yes, and it is the main practical difference between them day to day. Dry compound cleaning has no drying time, bonnet is under an hour, encapsulation is 20 to 60 minutes, and both extraction methods are 2 to 6 hours. Within extraction, the temperature of the water is not what sets the drying time. What sets it is how much moisture is left in the pile, which comes down to the number of dry-extraction passes, the airflow through the room and the humidity on the day.