Without further upgrading to Stronger Glue, Stickier Glue provides limited but useful help, although Stickier Glue greatly helps Stronger Glue due to inheriting the longer-lasting glue properties. For instance, it can be paired with Corrosive Glue to let more layers of normal bloon to pop before wearing out.
Stickier Glue remains unchanged since the game first came out.
Crosspathing in BTD6 (Top: Path 1, Bottom: Path 2)
Stickier Glue official upgrade icon in BTD6
In BTD6, Corrosive Glue without this upgrade can only pop a Rainbow down to Yellows without additional pops. Purchasing Stickier Glue will allow an entire Rainbow to be popped completely, provided that there's enough space for the Rainbow Bloon to go through the track without leaking. For pre-Round-80 Ceramics, a 2-0-1 Glue Gunner is able to pop the whole Ceramic layer without additional pops, but not the Rainbows inside.
Stickier Glue is the only BTD6 Glue Gunner upgrade moved to a different path compared to BTD5.