Trapunto has a filling at the back that raises parts of the design, the stuffing is cut back to the stitching lines - when hand embroidering it was stitched on a double layer of cloth and parts were raised by stuffing them from the back through small slits cut into the material at the back.

Embossed has a background grid to compress the pile of terry cloth or other material with a pile, and let the non-embroidered pieces stand out in relief.

Usually, the designs will be labeled whether they are trapunto or embossed. Look in the alphabets here on this site and Amazing designs and Cute Alphabets and there will be alphabets that are embossed. I have used the embossed alphabets with good success. They are high in stitch count, but worth the time and thread.

Thank you for your answers, I will try a embossed letter on a bath towel, I have seen very nice on cutealphabet.