From the Internet:
Longer overhangs are called cohesive ends or sticky ends. They are most often created by restriction endonucleases when they cut DNA. Very often they cut the two DNA strands four base pairs from each other, creating a four-base 5' overhang in one molecule and a complementary 5' overhang in the other.
So, there is no "substance" that is sticky. Instead, there are unpaired bases that can pair.