As a final test, why not just run the same amount of water through both filters without coffee grounds?

That'll maybe give an idea of how much resistance the filter shows liquid alone but it won't give any clues as to how/whether fine particles are clogging the paper & slowing the drain with a more open weave.

What are the purpose of the test? How grind size affects different filters, or to prove definitively that one filter draws slower than the other?

I would suggest the OP contact chemex. I too had a problem with slow draw down. Chemex knows about the issue and it seems to effect random batches if filters produced during a certain date range. Before contacting chemex, contact the merchant. Even if you recently purchased the filters, they might have been in the merchant's for a while. I purchased mine in easy summer or late spring.

Jay

unix04 wrote:What are the purpose of the test? How grind size affects different filters, or to prove definitively that one filter draws slower than the other?

To determine what causes one type of filter to draw down at a different speed to another, same dose, same grind, same brewer, same pour routine.

Then ideally you'd start with a control. Does either filter draw down slower with a constant amount of the same water. If so, you know it's a grind distribution interacting with the filter weave. If there is a difference prior to coffee being added, then it's clearly the weave size doing the work here. Remove variables until you don't see change, then add them until you do.