Plastic bank notes are made from a polymer, and have many advantages over the traditional paper notes.
Longevity: They last far longer (around 2.5 times) than the paper notes as the material is more durable. The plastic is not porous which means they do not absorb moisture and dirty- a huge benefit in hot, humid countries.
Security: They are far more difficult to counterfeit, and have many security features that the paper note does not.
Cost: They are cheaper to produce, and can be recycled.
Some countries that already have polymer notes:
Australia
New Zealand
Romania
Brunei
Papa New Guinea
As someone who has spent 5 years in New Zealand, I can tell you that my absolute favourite thing about plastic money is that it can go through the washing machine without any adverse affects! So no more panic when you realise you've left $20 in your pocket...