4" Carpenter memory foam behide your speakers ???

Yes basically that's it. They come in all sizes and also very large style body pillows. I would think that the larger size body type could be made into a very good tube trap.

Ive used in loudspeaker cabinets works fine if design calls for it.

HiFisoundguy may I ask you to be more specific with your finding. How did you mount them and did you use the memory foam pillows or? How large a foam did you use and placed directly behind speaker or up more towards ceiling.

Schipo I got a new memory foam mattress from Tempflow.com...the new King of memory foam mattresses and I used my other (76" by 60" Size carpenter memory foam mattress topper) to cut up and put behide my speakers. I cut some, about the same size as my vintage Sansui sp-5500 Horn speakers and let it (standed them right on the floor at the wall behide my speakers)...I did not hang it on the wall...(from the front of the foam to the back of the speakers) its about 11 1/2 inches on one side of the speaker and about 8 inches on the other side of the same speaker. It stayed right there too without tipping over.

I see so u purchased a whole memory foam mattress and used the memory foam topper to cut. Thats a an idea I will look into this. Thanks for the reply.