The Bank of Canada says its new $50 and $100 polymer bank notes will last much longer than the old paper-based versions. But that added durability doesn't mean they're indestructible.

Several reports have appeared about the new bills melting, crinkling or otherwise shrivelling after exposure to very high temperatures. 

On Tuesday, radio station CKFR in Kelowna, B.C., quoted a local credit union teller, Brittney Halldorson, saying staff at her credit union have seen the new bills melting in the summer heat.

"We're finding temperatures in cars, we've seen it a few times now, where three or four melt together," she told the station.

A woman in Cambridge, Ont., told the Cambridge Times last January that eight of the new $100 polymer notes shrivelled when her son put them in a tin that he placed near a heater.

So can the new polymer bills actually melt?

The Bank of Canada defends the hardiness of its new bills, pointing out that they last 2½ times longer than paper-based notes under normal conditions.

And when conditions aren't normal? 

'The Bank of Canada has seen no evidence that polymer bank notes have been affected by heat as described in recent news reports.' —Bank of Canada spokeswoman Julie Gerard

"The new polymer notes have been rigorously tested in very hot (over 100 C) and cold (under –60 C) temperatures to ensure their durability," says Bank of Canada spokeswoman Julie Girard in emailed remarks.  

"We put the notes in boiling water for over an hour and the notes retained their shape, size and properties, and could still be used as a means of payment," she says.

The bottom line? Polymer notes, like their paper counterparts, can't withstand every threat. 

"The Bank of Canada cannot rule out that polymer notes may be damaged in certain extreme conditions," Girard acknowledges. Just as paper-based bills can burn, polymer notes can also be damaged by very high heat. But the emphasis is on "very high".

As for reports that polymer bills left in hot cars can melt, the central bank is having none of it.

"The Bank of Canada has seen no evidence that polymer notes have been affected by heat as described in recent news reports," Girard says. "Bank notes printed on polymer material have been used in many countries for years, most of which have climates far hotter than in Canada," she points out. Australia, for example, has used polymer notes for more than 20 years.

But if you've somehow managed to stash some polymer notes near toasters or heaters, only to return to find your cash has morphed into something that doesn't resemble currency, don't panic. You can send the whole mess to the Bank of Canada. The central bank has a claim service that examines damaged or mutilated notes and can replace the bills.  

The central bank says it has processed only 40 cases of damaged polymer series bills involving 197 notes since the new series first appeared last November. While this is considerably less than the 3,000 paper-based cases processed in an average year, the polymer numbers will likely rise.

So far, polymer versions of the $50 and $100 notes are the only ones in circulation. New versions of the $20, $10, and $5 notes are set to roll out by the end of 2013.