Best furniture to act as bass trap

I think the above poster is thinking of a Tuned Membrane Bass Trap.  This is, of course, tuned.  The couch is not.

@rand-11  - yeah, totally understand.  It's not a tuned basstrap.  However, the 703 FRK is not a tuned bass trap either.  I'm just trying to say that there's some element of more efficient bass absorption when you place a flexible reflective material in front of a highly absorbive material (i.e. the 703 FRK).  It's not going to be perfect and it's not going to be a "tuned bass trap", but I would error on the side that there may be some benefit to the leather couch over the cloth couch. :)

The membrane better converts the longer wavelengths to heat energy than does the absorptive material. 

Toilets make a great bass trap. They are customizable too - depending where you sit and/or the fluid/solid levels you can tune them for the best sound. The only drawback is fitting the rest of your gear in the toilet - usually the door won’t close - audio is frustrating.

Seriously for good bass trap you need at least three if not four GIK corner traps. A large smooth leather sofa will be best. Cloth will absorb too much highs relative to lows.

Why do you think here's some element of more efficient bass absorption when you place a flexible reflective material in front of a highly absorptive material??

I agree with shadorne

measure first of course

DSP may be in your future...