I don't know exactly what and open cell is but I say sheepskin saddle cloth.
I regularly use a sheepskin under my other saddle blanket to prevent my horse from getting saddle sores - he is really prone to getting them and find sheepskins cheaper than a gel pad.
I'd say Sheepskin.
I use my Mattes pad regularly, my horse doesn't have a problem with his back but he just performs so much better when I'm riding in it. I also really like the Ecogold pads.