`...The Bank of Canada began circulating $100 polymer bank notes this week in an effort to combat counterfeiting and reduce costs. The plastic currency lasts longer and doesn't get dirty as quickly. "The tropical climate is a challenging environment for banknotes, especially because of high humidity and high temperatures," said polymer researcher Stane Straus. "This causes paper notes to absorb moisture, thus becoming dirty and limp quickly. Polymer notes, on the other hand, do not absorb moisture."