Wetting and then freezing the filters supposedly is supposed to keep the solution from having to saturate the filter so that in theory you lose less opiates to binding up in the filter. But in the end I found that using a tightly woven dress shirt with a high thread count was more effective in filtering out APAP and faster filtering than coffee filters. All around better. So I pre-wetted the shirt and froze it before filtering. Freezing your filtering device also helps keep the temp of your solution low thereby ensuring that the APAP settles out more easily without draining through. Coffee filters were also disappointing in how much APAP they let through and I felt like I needed a PhD in patience to wait for them to do their job.