No rebond or recycled materials crap.

Best you can afford

No rug under layment pad will hurt the floor so long ar is softer than the floor. To prove i refer you to MOH'S law and the scratch test http://geology.com/minerals/mohs-hardness-scale.shtml

You want to stay away from "rubber" or "latex" backing. You want to stay away from anything that is missing the "Safe for Hardwood" label.

Rubber/natural latex will discolour hardwood floor finish = orange stain under the rug which is almost impossible to remove without sand/refinish. Look for reputable rug dealers and look for the "safe for hardwood" badge.

thank you-almost all of them are latex or rubber-ugh