How to Specify Filter Foam: PPI, Density & Thickness Checklist for Buyers
How to Specify Filter Foam: A 5-Point Checklist for Buyers
GaoLeshi Technical Note | Reticulated Filter Foam | Updated 2026
Why a vague specification costs you money
Most filter foam problems start long before production — they start on the purchase order. A line that reads simply "20 PPI black foam, 500 pieces" leaves four of the five critical parameters undefined. Your supplier will fill the gaps with their own defaults, and those defaults may not suit your application.
The result is familiar: the foam arrives, looks correct, and then collapses under airflow, clogs in a week, or lets dust straight through. None of that is a manufacturing defect. It is a specification gap. This checklist covers the five parameters every filter foam order should carry.
The five parameters
Pore size — PPI (pores per inch)
PPI describes how many pores lie along one linear inch of foam. It is the single best predictor of what the foam will catch. Lower PPI means larger pores, higher flow, lower capture efficiency; higher PPI means finer capture but higher pressure drop. Our standard reticulated grades run 10–80 PPI, and activated-carbon-loaded grades extend to 10–100 PPI.
| PPI range | Filtration class | Typical applications |
|---|---|---|
| 10–15 PPI | Coarse pre-filtration | Large particles, lint, pond and agricultural intake |
| 20–40 PPI | General air and dust | HVAC pre-filters, air purifiers, equipment intake |
| 45–60 PPI | Medium-fine | Paint booth intake, cabin filters, dust collection |
| 60–80 PPI | Fine | Fine dust, mist separation, activated-carbon carrier |
| 80–100 PPI | Fine / carbon grades | Odour and VOC stages, precision instrument protection |
Density — kg/m³
Density is independent of PPI, and this is where most buyers get confused. A high-density foam can have coarse pores; a low-density foam can have fine pores. Density governs compression strength, dirt-holding capacity and service life — not what size of particle gets caught. Our filter grades are produced across 18–50 kg/m³.
| Density | Character | Trade-off |
|---|---|---|
| 18–25 kg/m³ | Lightweight, open, low pressure drop | Lower dirt-holding, shorter life, easier to clean |
| 25–35 kg/m³ | Balanced general-purpose grade | The default for most air and dust duties |
| 35–50 kg/m³ | High compression strength, high dirt-holding | Heavier, higher initial cost, longest service life |
Cell structure — reticulated vs. open-cell
Standard polyurethane foam is blown with closed cell windows that block airflow. Reticulation removes those windows through a controlled explosion process, leaving a clean open skeleton with porosity above 95%. If your application involves airflow or liquid flow, specify reticulated. If you need buoyancy, sealing or cushioning instead, closed-cell is the right choice.
Dimensions, thickness and tolerance
State the finished shape — sheet, roll, die-cut piece, tube or cylinder — plus thickness and the tolerance you can accept. Thickness directly drives pressure drop and dirt-holding: doubling thickness roughly doubles dirt-holding but also raises resistance. For cut parts, a drawing beats a description every time.
Compliance, colour and additives
Nominate any fire-safety requirement (we supply flame-retardant grades), colour (standard black, grey or white; custom on request), and whether the foam must carry an additive such as activated carbon. Sending the target standard with the enquiry avoids a second sampling round.
A specification you can copy
| Parameter | Your value |
|---|---|
| Material | Reticulated open-cell polyurethane (PU) |
| Pore size | ______ PPI |
| Density | ______ kg/m³ |
| Thickness | ______ mm (± ______ mm) |
| Size / shape | ______ mm × ______ mm, or see attached drawing |
| Colour | Black / grey / white / custom ______ |
| Flame retardancy | Not required / required to ______ |
| Quantity | ______ pcs (sample run ______ pcs) |
Three mistakes we see most often
Specifying PPI onlyNo density given
- Add density in kg/m³ to every enquiry
- If unsure, ask for the recommended grade for your duty
Confusing PPI with filtration efficiencyTwo different scales
- State the target particle size in microns if you know it
- Otherwise describe the application and let the grade follow
No tolerance on cut partsFit problems at assembly
- Give thickness tolerance explicitly
- Send a drawing for die-cut and shaped parts
Frequently asked questions
Can you recommend a grade if I only know my application?
Yes. Tell us the medium (air, water, oil mist), the flow rate and what you need to remove, and we will propose a PPI and density combination plus samples for confirmation.
Is higher density always better?
No. Higher density improves strength and dirt-holding but raises cost, weight and pressure drop. For disposable or frequently cleaned filters, a mid-density grade is usually the better economic choice.
What is the difference between PPI 20 and PPI 60 in practice?
PPI 20 passes far more air with less resistance and catches larger particles; PPI 60 captures much finer dust but needs more fan power and clogs sooner if used as a pre-filter.
Do you provide samples before bulk orders?
Yes. Samples can be produced in the PPI and density you specify so you can test before committing. You only cover the freight cost.