Embossing effects are more pronounced on thicker cardstocks. Generally speaking, past 18-point thickness, any paper thicker is produced by mounting multiple sheets together. If you mounted two (2), 18-point sheets together, that would be considered 2-ply and would result in a thickness of 36-points. Similarly, if you mounted three (3), 18-point sheets together, that would be considered 3-ply and would result in a thickness of 48-points. With that said, you do not want to emboss a single-layered card. First off, it would most likely only be 18-points in thickness and the embossing effect will not be very pronounced. Secondly, and most importantly, when you emboss a single layered card, the back side of a card will be affected by the embossing process. Embossing will show a reverse impression on the opposite side of the stock (deboss). So if you had any text on the backside in the same area being embossed on the front, it could make for unpleasant results.