Sticky Resin

Sticky Resin is the substance obtained by tapping Rubber Wood logs with a Treetap, and is rarely dropped when chopping Rubber Wood down.

Sticky Resin can either be smelted or extracted into Rubber (with the latter method producing more Rubber), or placed on the ground, where it acts similar to Soulsand and slows down all mobs and players.

Aside from that if you just think about the nature of a Sticky Resin, you might also find something else you can use it for...

As of version 1.64, all crafting recipes involving sticky resin have been changed to use rubber