Hello. It is not waterproof, no. The fabric is water resistant and water will bead up a bit in a light rain for a little bit but if you're planning to ride in sustained rain, we suggest something like our midweight Rain Jacket
. This windbreaker is more for chilly rides in the spring, summer and fall or for intermittent wind/rain rather than constant rain. It packs up very small to easily fit in your jersey pocket and this gives you the flexibility to bring it along if there are clouds and wind in the forecast, just in case you need it.
I hope that this helps, but please let us know if you have any questions at all.