Foam for oil and fluid duties.
Coarse liquid filtration, strainer elements, coolant separation and reservoir breathers — with a clear line drawn around what open-cell foam should and should not be trusted with.
Coarse separation, not fine filtration.
The same property that makes reticulated foam good at air makes it useful for liquids: a high-void lattice passes fluid with little restriction while catching larger contaminants through its depth rather than on a face. For strainers, pre-filters and breathers that is exactly what is wanted.
What it is not is a rated filter. If your specification calls for a micron rating, foam cannot honestly claim one, and it should sit upstream of a rated element as a pre-filter rather than in place of it. Used that way it earns its keep — taking the bulk load so the expensive rated element lasts several times longer.
- Suction strainers — keeping large debris out of a pump inlet.
- Reservoir breathers — filtering the air drawn in as fluid level drops, which is how most tank contamination actually arrives.
- Coolant and swarf separation — catching chips and fines in machine tool coolant returns.
- Pre-filters — protecting a fine element downstream.
- Drip trays and wicking — absorbing and holding fluid rather than filtering it.
Tell us the fluid.
"Oil" covers a very wide range of chemistry, and polyurethane's tolerance varies across it. Mineral oils and most water-based coolants are generally well tolerated. What attacks polyurethane is a different class: strong solvents, certain esters, and acids or alkalis at concentration. Get this wrong and the element does not merely stop working — it disintegrates into the system it was installed to protect.
So tell us the actual fluid, the operating temperature and the duty cycle. Three lines of information, and it changes the answer from a guess to an engineering judgement. If the combination is outside what we would stand behind, we will say so.
Polyether, even for liquids.
There is a real argument for polyester foam in liquid work: chemical reticulation leaves a rough, etched strand that grips fluid better by surface tension. For wicking and retention that is a genuine advantage.
But a fluid system is warm and wet by definition, which is precisely the condition under which polyester hydrolyses. For most oil-side applications polyether remains the safer engineering choice, and we would rather supply a filter that is slightly less good at holding fluid than one that turns sticky in eighteen months. See polyester against polyether.
Common questions.
Can reticulated foam filter oil as well as air?
For coarse duties, yes. The open lattice passes liquid with low restriction while catching larger contaminants through its depth, which suits strainers, pre-filters, coolant separation and reservoir breathers. What it is not is a fine hydraulic filter — if your specification calls for a micron rating, foam is the wrong medium and should sit upstream of a rated element rather than replacing it.
Does oil damage polyurethane foam?
Mineral oils and most coolants are generally well tolerated. What attacks polyurethane is a different class of chemistry — strong solvents, some esters, acids and alkalis. Tell us the fluid, the temperature and the duty cycle rather than just saying oil, because the answer varies substantially and getting it wrong means the element disintegrates into the system it was protecting.
Is polyester foam better for liquids?
For liquid retention specifically, its rougher strand surface does grip fluid better by surface tension. But polyester is vulnerable to hydrolysis in warm damp conditions, which is a real risk in a fluid system. For most oil-side applications polyether remains the safer engineering choice — see polyester against polyether.
Can foam oil filters be cleaned and reused?
Cleaning oil out of foam is harder than cleaning dust out, and it needs a solvent compatible with polyurethane rather than whatever is on the shelf. It is often practical for coarse strainer elements and often not worth the labour for fine ones. We will give you a straight answer for your specific fluid rather than a general claim.
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