Coccyx cushions come in all shapes and sizes but only one coccyx cushion uses Sciata® Foam; namely, the 2nd Gen. Sciata® Seat.  More than memory foam, Sciata® Foam's proprietary blend provides custom comfort for anyone wishing to sit more comfortably including those seeking relief from tailbone, tarlov cyst, or sciatic nerve pain. Sciata® Foam's ability to conform while providing support is best seen 1st hand but why not check out a video or two while you're here. 
Relax and realize relief.

Contemplating which seat would provide relief from that which ails you?  The short description is as follows: the CX is intended primarily for those with coccyx pain (a.k.a. tailbone pain or coccydynia ) or pain resulting from tarlov cysts while the SL and DL models address those with sciatic nerve pain (a.k.a. sciatica ).  The SL addresses a single leg with sciatic upset and can be rotated to address the affected limb while the DL is primarily for those with two troubled legs.  Those with no specific ailment who merely wish to sit more comfortably at work, home or play ought to give the CX a look. 
The graphic below (and the video above) both elaborate upon this explanation.

Our original video (directly above) provides some insight into the genesis of the Sciata® Seat and our ongoing quest to help those suffering from coccydynia and sciatic nerve pain experience some relief from their symptoms.  It also includes testimony from satisfied customers who have experienced relief from tailbone pain and other symptoms through regular use of our patented seat cushion.  Additional and more in-depth customer testimony can be found on our about page.  Those with questions are urged to check out our F.A.Q. section or ask us directly via the contact form.