This 12oz canvas pouch serves as a Pre-Filter for your Grayl purification system. This simple canvas bag allows you to increase the longevity of your Grayl filter by first ridding your water source of turbidity (scum, leaves, debris). Simply use your nesting cup to pour water through the canvas, catch the water in your Grayl container, and press per usual. You will be surprised at how much sediment and debris the canvas arrests before allowing water to go through the Grayl filter.
This will maximize the longevity of your Grayl system and the bag nests around the Grayl and fits into your nestable cup.