I haven't looked at the Triumph parts site lately, but used to be a standard and a gell pad available. Got my sissy bar used as a matched set with a gell seat and pillion. Sold the gell seat and pillion so still have a gell back rest pad. As far as I know, it's the same size as the regular version, but they probably don't even sell those any longer.
Update.... I did look at the site for you, the 44 part number matches the standard stock seat stuffing, and the 45 part number is the touring gell material. Looks like they do still sell the jelly version.