A wound filter cartridge is yarn spun in a crisscross pattern over a rigid core, deliberately wound loose on the outside and tighter toward the middle. That graded structure makes it a depth filter: dirt is captured all the way through the wall rather than only on the face, which is why it holds so much more sediment than it looks like it should.
How the winding actually traps dirt
Water enters through the loose outer layers, where the biggest grit is stopped first, then works inward through progressively tighter yarn that catches finer particles. Because loading is spread through the whole thickness, a wound cartridge keeps flowing long after a surface filter of the same rating has blinded off. That makes it the natural choice on a well with sand, silt or rust flakes, and a common first stage ahead of a softener or a carbon tank. The trade-off is that the rating is nominal rather than absolute, so a share of particles at the rated size will slip through.
Wound versus pleated versus melt blown
Pleated cartridges fold a flat medium into a star shape to create surface area, filter mostly at the surface, and can often be rinsed and reused a few times, which suits city water with light silt. Melt-blown cartridges are spun polypropylene with a similar depth structure to wound but a smoother, more uniform density and usually a lower price. Wound cartridges still win where the load is heavy and abrasive, and where high temperature or aggressive water rules out other media. If your housing keeps clogging within weeks, the answer is usually a wound or melt-blown depth filter at a coarser rating, not a finer one.
Picking a micron rating you will not regret
Start coarse. A single fine cartridge doing all the work plugs fast and starves the house of pressure. On visibly dirty water, run a coarse wound cartridge first and a finer one in a second housing behind it, so each stage removes what it is suited to. Fit pressure gauges before and after the housing: a growing gap between the two readings is the only honest signal of loading, far better than a calendar. Choose the finest rating that gives acceptable flow at your peak demand, not the finest rating on the shelf.
Iron, orange staining and change intervals
Wound cartridges are often bought because the filter keeps turning orange. That color is iron that has already oxidized into a particle. Penn State Extension notes that iron and manganese carry secondary, aesthetic standards with recommended maximums of 0.3 mg/L iron and 0.05 mg/L manganese, and that oxidized iron fouls softener resin, which is exactly why catching it upstream matters. A cartridge alone will not remove dissolved, still-clear iron: that needs oxidation and a proper iron filter, and a water test tells you which of the two you have. Our well water testing guide covers how to sample for it.
Questions people ask about wound filter cartridge
Can a wound cartridge be washed and reused?
Not reliably. Rinsing lifts surface dirt but leaves the particles held inside the depth of the yarn, so flow returns only briefly. Wound cartridges are consumables and are cheap enough to treat that way.
What micron rating should I start with?
On well water with visible grit, start coarse and add a finer second stage behind it. Fit a pressure gauge each side of the housing so you can see loading instead of guessing when to change it.
Why is my new cartridge orange within days?
That is oxidized iron loading the yarn. A cartridge catches iron only once it has turned to a particle, so recurring orange filters point to an iron problem that needs treatment upstream rather than a finer cartridge.
Will a wound cartridge remove chlorine or taste?
No. It is a mechanical filter and does nothing to dissolved chemistry. Taste, odor and chlorine need activated carbon, which is usually fitted as a second stage behind the sediment cartridge.