See this previous thread.

The vapour barrier under the slab will do a good job in limiting moisture drive into the basement. However, it does nothing for the temperature differential that will leave the slab cold in winter. So I would avoid using any carpet pad in a basement unless it's on top of Delta FL or equivalent or XPS and plywood.

Confession: For years in the '80s I did install basement carpet over pads; felt great on the tootsies and would hold up for the time it took to sell the homes, up to two years.

I'm not sure what it's called, but our installer used a felt-type breathable pad on the concrete under our carpeting. He said he used it all the time in basements because it didn't trap moisture. It was installed six years ago and still looks great.