Prefilters & Bioburden Control

Prefilters are a cost-effective, proven technology used throughout bioprocessing to remove particulates, reduce bioburden and improve processing efficiency. Our prefilter portfolio includes:
- Milligard® PES membrane prefilters: gamma-compatible, bioburden reduction filters supported by the Emprove® Program, and are the best choice for most pharma and biopharma applications.
- PolySep™ II or Milligard® prefilters: autoclave compatible and may provide the performance you need for more challenging applications.
All prefilters are:
- Offered in multiple pore sizes for efficient filtration of different process streams
- Available in OptiScale® formats for efficient screening and scaling
- Available in capsule and cartridge formats with multiple connection options for reliable scaling from bench- to production-scale processing
For help determining the right filter for your process, read our product selection guide.

Milligard® PES Filters
Milligard® PES filters offer polyethersulfone (PES) membranes in three pore sizes. These prefilters increase the capacity of sterilizing filters or protect unit operations from particulate impurities. They can also be used as standalone bioburden reduction filters in processing steps that may not need a sterilizing filter.
Key Benefits
- Validated bioburden reduction claims (1.2/0.2 µm nominal, 1.2/0.45 µm only)
- Fast flow and high throughput
- Available in gamma-compatible formats, that can be integrated into Mobius® single-use assemblies
- Available in capsule and cartridge formats
- Supported by the Emprove® Program

PolySep™ II Filters
- Mixed media of borosilicate glass microfiber and mixed esters of cellulose.
- Pore sizes: 1.0/0.2/0.1 μm, 1.0/0.2 μm, 1.0/0.5 μm, 1.0/1.2 μm, 2.0/1.2 μm.
- High capacity prefilters for removing particles from plugging, viscous, and challenging streams.
- Available in both capsule and cartridge formats.
Milligard® Filters
- Mixed esters of cellulose on a polyester web.
- Pore sizes: 0.2 μm, 0.5 μm, 1.2 μm, 0.5/0.2 μm, 1.2/0.5 μm.
- High particle and retention capacity prefilters for use upstream of sterilizing filters.
- Available in both capsule and cartridge formats.
Our Tech Note shows comparative performance of Milligard® PES filters with Polysep™ II and Milligard® filters.
Compliance
Milligard® PES, Milligard® and Polysep™ II filters are designed, developed, and manufactured in accordance with a Quality Management System approved by an accredited registering body to an ISO 9001 Quality Systems Standard, and supported by a certificate of quality.
Each Opticap® XL, XLT, T-line, Small Scale 300 capsule and cartridge filter is supported by a validation document for compliance with regulatory requirements. For traceability and easy identification, each filter is marked with identifying characteristics.
Related Articles
- Aseptic filters are offered in disposable capsules and cartridge formats. This guide will help you find the right format for your bioburden control.
- Discover various Millipore Express® sterilizing-grade membrane filters for liquid filtration in aseptic drug production.
- Prefilters can be used throughout bioprocessing to remove to remove particulates, improve quality and protect sterilizing filters and downstream unit operations.
- Some prefilters reduce bioburden and can be used as a cost-effective alternative to sterilizing filters for bioburden control in bioprocessing.
Related Documents
- Prefilter Family Guide
Discover cost-effective membrane-based prefilters that protect downstream operations, improve sterilizing-grade filter capacity, and reduce area requirements for enhanced process economics.
- Technical Note: How Membrane Prefilters Enhance Bioprocessing Efficiency
Milligard® PES filters improve sterilizing-grade filter capacity and process economics
- Technical Note: Bioburden Reduction and Particulate Retention Using Milligard® PES Filters
Learn how Milligard® PES filters can be used as standalone filters in less critical process steps to remove particulates, reduce bioburden and provide high throughput.
- White Paper: Sizing Up Successfully
Best practices for sizing sterilizing-grade filters for aseptic manufacturing of sterile drug products.
- Application Note: Processing mAb streams. How a bioburden reduction filter can improve process efficiency
For downstream processing steps that require bioburden control, rather than sterilizing-grade filtration, Milligard® PES filters are an attractive option.

