Home › Blog › Medical › Medical Fluid Management & Filtration › Material selection
Reticulated Foam, FFKM, or Medical Silicone: Choosing Fluid-Management and Filtration Materials
Fluid-management parts split into two jobs that get confused because both can look like a foam or a gasket: moving a fluid, by wicking or filtering it through an open-cell structure, and containing a fluid, by sealing a path with a closed-cell or solid elastomer. They need opposite cell structures, so the first task is to name whether the part moves fluid or contains it. The families on the H-O fluid page sort by exactly that, and this guide walks each by the decision it wins, with the reagent named first.
Move it or contain it: name the job first
An open-cell reticulated foam moves fluid: its interconnected pores wick a sample, absorb a reagent, or filter particles from a flow, and it is chosen for pore grade and chemical compatibility. A closed-cell or solid elastomer contains fluid: its job is to seal a path so the fluid goes where it should and the seal does not contaminate it, and it is chosen for chemical resistance and the biocompatibility basis.
Specifying a closed-cell gasket where a wicking foam belongs blocks the flow it was meant to carry, and specifying an open-cell foam where a seal belongs leaks the fluid it was meant to contain. So the families sort by job, with the reagent or solvent named first, because compatibility governs both.
Moving fluid: reticulated foams
Where a diagnostic cartridge has to wick a sample or absorb a reagent, a biocompatible reticulated PU foam is the default: its open, reticulated cell structure draws fluid by capillary action and its maker publishes a biocompatibility basis for fluid contact.
Where the part filters particles from an air or fluid path rather than wicking, an uncoated reticulated PU foam is chosen to a pore grade, and a coated reticulated foam adds a surface treatment where a cleaner pore face or a particular wettability is wanted. The pore grade, stated as pores per inch, sets how the foam wicks and what it filters, and choosing it is the subject of the companion design article on this estate.
Containing fluid: medical silicone and FDA-grade elastomers
Where a fluid path has to be sealed without the seal shedding into the fluid, a medical silicone is the workhorse, chosen for its clean fluid contact and its biocompatibility basis, and an FDA-grade white or translucent elastomer seals a path where a lower-cost food-and-drug-contact grade suffices and the reagent is mild. A silicone foam seals or cushions a lab-equipment fluid interface at low closure force.
The seal is chosen so the material is compatible with the fluid it touches, because an incompatible elastomer swells, hardens, or leaches, which the companion design article walks in detail.
The aggressive reagent: FFKM
Some reagents and solvents attack silicone and standard elastomers, and where the fluid path sees an aggressive chemistry the seal moves to a FFKM with a USP Class VI and FDA medical grade. FFKM is the most chemically resistant elastomer family, holding a seal against solvents and reagents that would swell or degrade a silicone, while still carrying a published biocompatibility basis.
It is the premium choice reserved for the chemistries that defeat the workhorse materials, so it is specified once the reagent is named and shown to be incompatible with the lower-cost options.
Fluid-Management and Filtration Families by Job
| Family | Job | Cell / form | Reagent latitude | Where it lives |
|---|---|---|---|---|
| Biocompatible reticulated PU | Wick / absorb | Open-cell, reticulated | Aqueous, mild | Cartridge wicks, reagent pads |
| Uncoated reticulated PU | Filter | Open-cell, pore-graded | Air, mild fluids | Particle filtration paths |
| Medical silicone | Seal fluid path | Solid / closed-cell | Aqueous, many reagents | Fluid-path gaskets |
| FDA-grade elastomer | Seal mild path | Solid elastomer | Mild reagents | Low-cost fluid seals |
| FFKM (USP Class VI) | Seal aggressive path | Solid elastomer | Aggressive solvents | Harsh-reagent fluid paths |
Illustrative and relative only; confirm each grade and its chemical compatibility on its current TDS. Biocompatibility basis per the ISO 10993 series and USP Class VI; a reticulated foam is a wicking or particle-filter medium, not a sterile or absolute filter.
Two rules that sort the page
First, match the cell structure to the job: an open-cell reticulated foam moves fluid and a closed-cell or solid elastomer contains it, and confusing them either blocks the flow or leaks the path. Second, name the reagent before anything else, because chemical compatibility governs both the foam and the seal, and an incompatible material swells, hardens, leaches, or stops wicking, which the companion design article on this estate walks in detail. Pick the cell structure to the job, then the chemistry to the reagent.
How H-O Products helps
H-O Products is a precision die-cut converter, not a raw-material producer and not the device maker. We take biocompatible and uncoated reticulated PU foams, coated reticulated foam, medical silicone, FDA-grade white and translucent elastomers, silicone foam, and USP Class VI FFKM from the material manufacturers and die-cut, kiss-cut on liner, laminate, and kit them to your drawing, with material traceability and lot-code TDS records under our ISO 9001:2015 certified quality management system in Winsted, Connecticut.
We recommend a family from whether the part moves or contains fluid, then the pore grade or the seal chemistry from the reagent you name, with grade-level values confirmed against the maker's current TDS. Filtration validation, biocompatibility testing per the ISO 10993 series, and device clearance stay with the device owner.
Frequently asked questions
What foam absorbs and wicks a sample or reagent in a diagnostic cartridge?
An open-cell reticulated polyurethane foam, chosen to a pore grade and to a biocompatible grade where it contacts a sample. Its interconnected pores draw fluid by capillary action, so it wicks a sample or absorbs a reagent. A biocompatible reticulated PU foam carries a published biocompatibility basis for fluid contact on the maker TDS. The pore grade sets how fast and how much it wicks, which the companion design article on this estate covers.
How do I choose the pore grade (PPI) for a filtration or wicking foam?
By what the foam has to do. A higher pores-per-inch foam has finer, more numerous pores, which wicks more strongly by capillary action and traps smaller particles but flows more slowly; a lower PPI flows faster and traps larger particles. So a wicking pad and a coarse particle filter want different PPI. Tell us whether the part wicks or filters and the flow and particle target, and we recommend a pore grade. The companion design article walks the PPI trade in detail.
What seals a fluid path so the seal does not contaminate the fluid?
A medical silicone or an FDA-grade elastomer chosen for clean fluid contact and compatible with the reagent it touches. Medical silicone is the workhorse for many aqueous and mild-reagent paths and carries a biocompatibility basis; an FDA-grade white or translucent elastomer suits a lower-cost mild path. The seal is chosen so it does not swell, harden, or leach into the fluid, which means the reagent is named first and the material confirmed compatible against its TDS.
Open-cell vs closed-cell foam: how do I tell which I need?
By whether the part moves fluid or contains it. An open-cell foam has interconnected pores that let fluid through, so it wicks, absorbs, and filters; a closed-cell foam has sealed cells that block fluid, so it seals and cushions. If you want the part to carry or filter fluid, it is open-cell; if you want it to keep fluid out or in, it is closed-cell or solid. Specifying the wrong one either blocks the flow or leaks the path.
Can an adhesive backing be added without blocking the wick?
Yes, by keeping the adhesive off the wicking faces. We laminate an adhesive to a non-wicking surface of the foam, or pattern it so the capillary path stays open, and kiss-cut the part on a liner for placement. The key is that the adhesive must not seal the open-cell faces that do the wicking, so tell us which faces draw fluid and which mount, and we place the adhesive so it holds the part without blocking the flow.
How does H-O document the biocompatibility basis for a fluid-contact part?
We convert materials whose makers publish a biocompatibility basis and pass it through with traceability. The maker TDS for a biocompatible reticulated foam, a medical silicone, or a USP Class VI FFKM names the relevant ISO 10993 series endpoints, such as cytotoxicity, sensitization, and irritation, and USP Class VI where applicable, and we supply material traceability and lot-code records referencing that data sheet. H-O does not perform biocompatibility testing and does not certify the device; that belongs to the device owner.
Is a reticulated foam a sterile or absolute filter?
No. A reticulated foam is a wicking or particle-filter medium: it moves fluid and traps particles by its open-cell pore structure, but it does not carry a validated sterilizing-grade or absolute-rated filtration claim. A sterilizing or absolute filter is a membrane and a validated device function. H-O converts the foam to the pore grade and geometry you specify; the filtration validation and any sterility claim stay with the device owner and its test houses.
Which seal material handles an aggressive solvent or reagent?
A USP Class VI FFKM, the most chemically resistant elastomer family, which holds a seal against solvents and reagents that would swell or degrade a silicone while still carrying a published biocompatibility basis. It is the premium choice reserved for chemistries that defeat the workhorse materials, so it is specified once the reagent is named and shown incompatible with the lower-cost options. Name the reagent and we confirm compatibility against the TDS.
Are reticulated foam fluid parts single-use or can they be sterilized and reused?
Most reticulated-foam fluid parts in cartridges are single-use, because the wicking medium captures the sample, but the device design determines that, not the material alone. If the part is reprocessed, the sterilization route and cycle count are named so the foam and any seal are confirmed to tolerate them. Tell us whether the part is single-use or reprocessed and we select and convert accordingly; the sterilization validation stays with the device owner.
Can H-O laminate a foam pad to a film backer or a coated barrier?
Yes. We laminate a reticulated foam to a film backer, a coated barrier, or an adhesive, and die-cut and kiss-cut the assembly to your drawing, keeping the wicking faces open where they need to draw fluid. Send the layer stack and which faces wick and which mount, and we build the laminate and cut it to your geometry with material traceability.
Does H-O make finished medical devices or certify the fluid path?
No. H-O converts the documented foams, seals, and elastomers to your drawing, with material traceability and lot-code TDS records that support your file. Designing the cartridge or fluidics, validating the filtration, performing biocompatibility testing per the ISO 10993 series, and holding device clearance belong to the device owner and its test houses. Our role is bounded: die-cut, kiss-cut, laminate, and kit the parts to your drawing, repeatably and traceably.
What do I send H-O to get a fluid-management or filtration quote?
Tell us whether the part moves fluid or contains it, name the reagent or sample and any solvent, and send the geometry, the pore-grade or flow target for a foam, the closure force for a seal, whether the part contacts a sample, any biocompatibility basis needed, and the quantities. With that, engineering recommends a family and grade and quotes a die-cut part. The companion how-to-spec article on this estate is a full checklist.
Get a fluid-management or filtration recommendation
Tell us whether the part moves or contains fluid, name the reagent or sample, and send the geometry and the pore-grade or closure-force target, and we will recommend a family and grade and quote a die-cut part to your drawing.
Samples typically ship in 3 to 5 business days for common die-cut configurations on materials we keep on hand; standard production runs about two weeks after drawing approval; expedited service is available. MOQ varies by material and part.
Family-owned in Winsted, Connecticut since 1971 · ISO 9001:2015 certified · OEMs worldwide send us a drawing — and get back their part.
Related reading
Request a quote for your medical fluid-management part
Send H-O the fluid-path geometry and the reagent—engineering reviews every RFQ and converts samples on your geometry.
Last updated · Reviewed by H-O Products engineering (ISO 9001:2015 certified converter, Winsted, CT).
References
- ISO 10993 series (biological evaluation of medical devices: cytotoxicity, sensitization, irritation endpoints), cited by designation as the biocompatibility basis named on each maker data sheet.
- USP Class VI (plastics biological reactivity classification), cited by designation where named on the maker TDS, including the FFKM grade.
- Manufacturer technical data sheets and chemical-compatibility data for the biocompatible and uncoated reticulated PU foams, coated reticulated foam, medical silicone, FDA-grade elastomers, silicone foam, and USP Class VI FFKM grades named on the parent application page.
This article summarizes material-selection and design principles for medical fluid management and filtration using the families and published test methods cited on the parent application page. Comparisons are qualitative; per-grade values are maker technical-data-sheet figures and must be confirmed on the manufacturer's current TDS at your installed condition. Standards (ISO 10993, USP Class VI, ISO 11607, IEC, ASTM, UL) are cited by designation for context, not as a claim of qualification or registration.
H-O Products is a precision die-cut converter, not a raw-material producer and not the device maker; biocompatibility testing, sterilization validation, device clearance, and final-assembly certification belong to the device owner and its test houses.