Envelope filter bags are custom-shaped filtration bags used when a standard cylindrical filter bag does not match the equipment, basket, frame or process requirement.
INCE filtration supplies custom envelope filter bags for industrial liquid filtration based on customer drawings, samples and technical specifications. Available customization can include filter media, micron rating, width, length, opening style, seam construction, edge finishing, labels and packaging.
For standard cylindrical liquid filter bags and broader OEM programs, see our OEM Filter Bag Manufacturer page.
What Is an Envelope Filter Bag?
An envelope filter bag is a flat or rectangular filter bag construction designed for equipment where a conventional round bag is not suitable.
The exact shape varies by machine and application. Typical envelope-style designs may use:
- Flat rectangular bodies
- Custom widths and lengths
- Open-top or partially closed openings
- Sewn or folded edges
- Drawstring, stitched or reinforced openings
- Custom attachment or support details
Because there is no single universal envelope size, these bags are often manufactured from a drawing, sample or equipment dimension.
Custom Envelope Filter Bag Manufacturing
INCE filtration can evaluate envelope-style filter bag projects according to the actual filtration requirement and equipment geometry.
Important customization parameters include:
- Bag width
- Bag length
- Opening width and construction
- Filter media
- Micron or mesh rating
- Seam method
- Edge reinforcement
- Operating temperature
- Liquid being filtered
- Required quantity
- Packaging and labeling
For non-standard designs, the most reliable starting point is an engineering drawing or physical sample.
Available Filter Media
Polypropylene Filter Media
Polypropylene filter media is widely used for economical industrial liquid filtration where the chemical and temperature conditions are compatible.
PP felt or compatible PP constructions may be considered for:
- Water treatment
- Chemical processing
- Paints and coatings
- General process liquids
- Industrial pre-filtration
Polyester Filter Media
Polyester filter bags provide good mechanical strength and abrasion resistance and may be selected for applications requiring greater durability.
Nylon Mesh
Nylon mesh filter bags are useful for surface filtration and particle screening where a defined mesh opening is required.
For envelope-style mesh bags, the mesh opening, fabric orientation, seam style and final dimensions should be confirmed before production.
Micron and Mesh Rating Options
The filtration rating depends on the selected media.
Felt constructions are typically used for depth filtration, while woven mesh is generally used for surface filtration.
Common industrial liquid filtration ratings may include:
- 1 micron
- 5 micron
- 10 micron
- 25 micron
- 50 micron
- 75 micron
- 100 micron
- 150 micron
- 200 micron
- Coarser mesh openings where required
The correct rating should be selected according to the particle size to be retained, flow requirement, solids loading and required service life.
Envelope Filter Bag Seam Options
Seam construction is especially important for custom-shaped bags because the seam must maintain the required geometry while limiting bypass.
Depending on the media and application, envelope filter bags may use:
- Industrial sewn seams
- Folded seams
- Reinforced stitched edges
- Compatible thermal welding for suitable synthetic media
The final method should be selected after confirming the filter media, liquid, operating temperature and required cleanliness.
Custom Openings and Edge Construction
Unlike standard Size #1 or Size #2 filter bags, envelope bags may use many different opening structures.
Possible configurations can include:
- Simple open top
- Folded opening
- Drawstring opening
- Reinforced fabric edge
- Custom stitched attachment
- Special opening geometry according to the machine or basket
When replacing an existing bag, provide clear photographs and opening dimensions in addition to the overall width and length.
Can You Copy an Existing Envelope Filter Bag?
In many cases, yes.
If the original drawing is unavailable, INCE filtration can evaluate a project from:
- Physical sample
- Detailed photographs
- Overall width and length
- Opening dimensions
- Material information
- Micron or mesh rating
- Existing part number
- Equipment model
A physical sample is preferred for non-standard designs because small differences in seam allowance or opening construction can affect fit.
Industrial Applications
Custom envelope filter bags may be used in industrial equipment where a flat or rectangular filtration element is required.
Typical project areas can include:
- Industrial liquid straining
- Process-water filtration
- Chemical production
- Paint and coating filtration
- Food-process straining where compatible materials are specified
- Equipment-specific filtration
- Custom OEM filtration systems
Material suitability should always be confirmed against the actual liquid, temperature and operating conditions.
Envelope Filter Bag Supplier for OEM Equipment
Equipment manufacturers may require a filter bag that matches a proprietary basket, frame or filtration chamber.
For these projects, INCE filtration can review:
- Equipment drawings
- Basket dimensions
- Opening geometry
- Required filtration area
- Media specification
- Seam and edge details
- Packaging and part-number requirements
Once the design is confirmed, the approved specification can be used as the reference for repeat production.
Private Label and OEM Packaging
For distributors and filtration brands, custom packaging can be added to the envelope filter bag program.
Options can include:
- Customer labels
- Part numbers
- Custom packing quantity
- Carton marks
- Private-label packaging
Packaging requirements should be confirmed together with the filter bag specification before batch production.
What Information Is Needed for a Quote?
For a custom envelope filter bag quotation, send:
- Bag width
- Bag length
- Opening dimensions
- Filter media
- Micron or mesh rating
- Seam requirement
- Liquid being filtered
- Operating temperature
- Estimated quantity
- Drawing, photos or sample
- Packaging or labeling requirements
If some information is unknown, send the existing bag or equipment drawing so the specification can be reviewed.
Envelope Filter Bag FAQ
What is an envelope filter bag?
An envelope filter bag is a flat or rectangular filtration bag made for equipment where a standard round filter bag is not suitable.
Can envelope filter bags be made to custom dimensions?
Yes. Width, length, opening structure and seam construction can be customized according to the equipment or sample.
What materials are available?
Common project materials include polypropylene, polyester and nylon mesh. Final selection depends on the liquid, temperature and filtration requirement.
Can you manufacture from a sample?
Yes. A physical sample can be used to evaluate dimensions, seam construction and opening details when an original drawing is unavailable.
Can the micron rating be customized?
Yes. Available filtration ratings depend on the selected felt or mesh media.
Do you support OEM and private-label orders?
Yes. Custom labels, part numbers, packing quantities and private-label packaging can be reviewed as part of an OEM project.
Request a Custom Envelope Filter Bag Quote
Send INCE filtration your drawing, sample, dimensions, filter media, micron rating and required quantity.
We can review the specification and prepare a custom envelope filter bag solution for industrial filtration and OEM equipment applications.
Contact INCE filtration for an envelope filter bag quotation.
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