The short answer is, "probably". But it does depend on just how wet the warmers get. The warmers generate heat via a chemical reaction which is catalyzed by air flowing through tiny holes in the pouch. A large amount of water can block the airflow to the contents of the pouch, impeding that reaction. The warmers will not work well, if at all, if they are submerged or totally saturated. On the other hand, light to moderate rain, or the amount of moisture that might be generated by sweat or a bit of snow melting on your gloves, is not likely to impede the function of the warmers significantly. If your warmers do get very wet and it seems like they are not working adequately, drying them off and then giving them a vigorous shake should get them working, though they still may not give off quite as much heat as fresh dry ones.