I don't know which type it is, but I highly reccomend Norton 3x paper. The dust tends to fall off rather than pack into the paper, and it really does cut better & last longer.

That's aluminum oxide.  Thanks Jim.

I recently went to my local big-box home center to replenish my supply of Norton 3X, and they seem to have discontinued that product line. So I bought what they had, Diablo brand, with holes configured for all the different disc sanders. I have to say, I was blown away by the quality of this sandpaper. Much faster cutting than Norton 3X, much longer lasting, much less dust retention, and much less buildup of gummy glaze. Just my opinion, but I am a convert.

Jim