Felt and mesh are the two workhorse medias of bag filtration, and the choice between them decides more about your results than any other spec on the order. We manufacture both, in every standard size, so we have no thumb on the scale — here’s how the two actually differ, and how to pick.
Two Different Ways to Catch a Particle
Felt is depth media. A needled mat of fibers captures solids all the way through its thickness — particles wedge into progressively tighter passages, and the bag keeps working as it loads. That’s why felt tolerates heavy, variable dirt loads and reaches tight nominal ratings. Mesh is surface media. A woven screen with a uniform, engineered opening stops everything larger than the hole right at the face — a true geometric cutoff, and a cake of solids you can see, wash off, and even reclaim.
The Short Version
| Felt filter bags | Mesh filter bags | |
|---|---|---|
| Micron range | 1–200, nominal | 35–800, true cutoff |
| Rating behavior | Nominal — majority capture, improving as cake builds | Absolute-style geometric cutoff — nothing larger than the opening passes |
| Dirt-holding capacity | High — loads throughout the media depth | Lower — blinds when the surface cakes over |
| Reusable? | No — washing removes surface cake but not embedded solids | Yes — wash out the cake and return to service |
| Product recovery | Solids are absorbed into the media | Cake sits on the surface — capture and reclaim it |
| Fiber shedding | Minimal with glazed (singed) finish | Essentially none — no loose fibers to migrate |
| Cost profile | Lowest cost per gallon in dirty streams | Higher per bag, but reuse can win the long game |
| Medias | Polyester, polypropylene, Nomex®; FDA grades | Nylon monofilament (NMO), polyester multifilament; FDA grades |
When Felt Wins
Choose felt when the rating must be tighter than 35 micron — mesh simply isn’t woven finer in bag service — or when the stream carries real dirt load: coolant, wash water, paints, plating baths, wastewater. Depth loading means longer runs between change-outs at the 15 PSID rule, and felt’s cost per gallon filtered is the lowest of any common format. Glazed finishes limit fiber release; welded construction eliminates needle-hole bypass when trace leakage matters.
When Mesh Wins
Choose mesh when the cutoff has to be exact, when the solids are the product — catalyst recovery, food straining, reclaim duty — or when disposal costs make a washable, reusable bag the cheaper system. Mesh is also the answer where fiber shedding is a defect: no depth media means no loose fibers downstream. In the 35–200 micron range where the two overlap, the tiebreakers are dirt load (heavy → felt), reuse economics (frequent change-outs of light loads → mesh), and whether “nominal” is acceptable to the process (if not → mesh).
Or Use Both
The formats combine well. A coarse mesh bag ahead of a fine felt bag knocks down bulk solids and stretches felt life in heavy streams. And felt bags can be ordered with a mesh outer cover — a nylon or polyester screen sewn over the felt — where cake release and handling matter. Both are standard order options, not specials.
Still on the fence? Tell us the fluid, flow, solids, and target clarity — quote form or 800-554-8555 — and we’ll spec the media with you. We make both, so the answer is whatever actually works.