So I couldn't resist the good idea to do a cross section of a Savinelli filter. I had a 6mm filter from a few weeks ago - single use - that was dry. I did a comparison with an unused filter. The tobacco was Lane Limited Ready Rubbed.
Looking at the photos, it is pretty clear that the tar does not filter into the balsa wood, though there is an awful lot of tar on the outside of the filter. Also, sucking on the balsa does not draw the same as sucking on a 9mm Charcoal filter. Sorry, no pictures of my mug doing that. But it does draw. When I do t use a filter there is a strong and long lasting tobacco aftertaste in my mouth, which my wife is more than ready to remind me of. When I use a charcoal filter, there is virtually no aftertaste, and when I use a Savinelli filter there is somewhere between half and a third of the filterless aftertaste. Seeing the physical evidence of tar on the filter and knowing this experience, I (non-scientifically) determined that the filters remove tar, though I don't know how much. I don't have a baseline for how much tar is in a smoke, though that is an assload more tar than was ever held by a cigarette filter that I'd smoked (yes, assload is a scientific term).
What is most telling to me is the very significant yellowing of the filter - that is mostly nicotine left in there after the filter dried. I can also tell you, if I get too much nicotine, my face turns red. It does not do that when using a Savinelli filter, so I know from both the visual evidence and my experience (again anecdotal and non-scientific)that it is drawing off a significant amount of nicotine.
Now, Savinelli claims to have used two independent testing companies which determined that the filters remove "up to" 77% of the nicotine and 91% of the tar. Note the control of language on the site - the claim isn't removes, but rather up to. So you don't know the circumstances. Still, it is obviously removing both tar and nicotine, from both a visual and experiential standpoint. Another bonus, as stated above, is that tongue bite is virtually eliminated while maintaining flavor.
As with all things opined upon in these illustrious digital pages of pipedom, YMMV. But the filters are good to go and effective for me.
On to the pics:
The filters, side by side.
A close up, note the uniform yellowing, but also the spotty tar deposits, the latter demonstrating the absorbing discussion from above:
Some close ups:
And some cross sections. One cut perpendicularly, one cut horizontally, both showing a lot of nicotine discoloration inside the balsa, but no tar discoloration:
I will conclude with 2 points: as with all things pipe, it is an individual experience and your own subjective view is the most important. So try things out if they interest you and see for yourself. These pages are filled with people who are more than happy to tell you the way it is from their perspective as though it were the gospel, and as with everything, it is never always that. My own opinions included.
Second, my wife is immeasurably pissed at me for spending all of this time with a nasty used filter and writing this up. So . . . gotta go!