Benefits: 
Zipper closure, all made of plastic
Rigid seams to prevent leakage of filter media from the bag
Very fine synthetic material, 250 microns that allows water to circulate easily
Can be reused multiple times
The material is not affected by chlorine or acids
It keeps its flat shape, which helps the water to have a good contact with the entire contents of the bag
Recommendations : 
Make sure the zipper is fully closed
Keep the filter media inside and only rinse with water
Do not use sharp-edged filter media
Use size S for about 250 ml of filter media
Use size L for about 500 ml of filter media