What makes an epoxide stable?

Overall ring strain seems to be a big issue when it comes to organic chemistry. That is why cyclopentane may be in an "envelope form" or why cyclobutane may be in a kinked, kite form. Both of these example molecules are not planar. So, why is epoxide (oxacyclopropane) a stable molecule, if at all?

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Chemists talk about conformation, not "form". What do you mean by "stable"? Epoxides seem pretty reactive to me :) – CHM Apr 30 '12 at 0:42
""a stable molecule, if at all?"" Do You doubt the existence of epoxides? Some molecule being stable without giving conditions means "You can fill that in a bottle and it will suvive for some days at least" in lab slang. – Georg May 1 '12 at 12:28
You could say it is kinetically stable, but thermodynamically unstable. – user95 Jul 12 '12 at 5:18

$\newcommand{c}[1]{\mathsf{\small #1}}$ You can't quite compare rings consisting only of carbon atoms with rings with oxygens in them. In the latter, the $\c{C}-\c{O}$ bonds are polar, the electrons are closer to the oxygen atom which means the acuteness at the $\c{C}$ atoms is not as much of a problem as it would be in a hydrocarbon ring.