Frequently Asked Questions

Sterlitech PES (polyethersulfone) membranes are asymmetric, meaning the largest pores are on one side and the smallest pores are on the opposite side. You can identify the sides by viewing the membrane under reflected light at a low angle—the larger-pore side looks dull/matte, while the smaller-pore side appears shinier/smoother.

The membrane can be installed either way without changing retention, but for best results:

Dull/matte side upstream = higher flow and throughput
Shiny side upstream = better surface capture for microscopy/particle analysis

Sterlitech PES (polyethersulfone) membrane filters have an asymmetric pore structure, meaning one side has larger pores and the other has smaller pores. To identify the correct side, view the membrane under reflected light at a low angle—the larger-pore side appears dull/matte, while the smaller-pore side looks shinier/smoother.

For maximum flow rate and throughput, orient the filter with the dull/matte (larger-pore) side facing upstream. For microscopy or particle capture, you may place the shinier (smaller-pore) side upstream to keep particles closer to the surface (with reduced throughput).

PES (Polyethersulfone) membrane filters offer very low protein binding and high flow rates, making them ideal for sterile filtration of tissue culture media, buffers, and other life science and microbiology fluids. PES membranes provide excellent throughput, broad chemical compatibility, and reliable performance for cell culture media sterilization and routine laboratory filtration applications.