I have a nylon rain jacket that I wear to walk my dogs when it rains. It seems that no matter what clothes I wear underneath, I always end up very sweaty. I've tried long sleeves, short sleeves, quick-dry and cotton shirts, but it just happens after about 10 minutes. Of course, Texas weather is generally hot anyway, but still..
Does anyone have tips for avoiding or lessening sweating while wearing a rain jacket?
Staying dry in a rain jacket requires you to sweat less moisture than the cloths you are wearing can breath out.
The most effective way to let moisture out is ventilation, unfortunately, that means holes big enough to let water in -e.g. cotton. With a rain coat, apart from wearing it open, Pit zips (zips under the arms) are a very effective way to get a lot of ventilation without letting too much water in (even some very good breathable jackets have them.). The extreme form of a well ventilated rain coat is an Umbrella :) .
The alternate is what are known collectively as breathable fabrics that let water vapour though the fabric, but not water. Goretex is probably the most well known as it was the first to be widely commercialised (It came out of the NASA space program), but there are many others now.
Choosing a fabric is really a trade off between breathability, water proofness, robustness, and cost. Choose three, accept the fourth. Goretex has different fabrics suited for different tasks, with different pricing.
Humidity significantly affect how breathable a particular jacket is on a given day. If humidity is high and its warm, forget about staying dry, even the very best jacket will not breath enough and you might as well wear nylon (or nothing). If its cold and dry, even a cheap breathable jacket will breath well enough to keep you dry. If the outer layer has water build up on it, the jacket won't breath - new jackets have coating (DWR) that makes the water bead up and run off.
In the end, some days you are just going to get wet, and the only thing you can do to stay dry is stay home. The more you spend, the fewer of these days you get. Some days, its just as easy to leave the raincoat at home and wear cloths that keep you warm even if you are wet.
Unfortunately there isn't much you can do if your rain jacket is not breathable. My recommendation is to replace your rain jacket with a poncho, which may be very cheap - while a highly breathable rain jacket cost hundreds of dollars. A poncho is much more ventilated than any jacket and will allow the moisture to leave your body by leaving it way drier; especially for an activity that is not physically demanding as walking the dog.
The drawback of using a poncho is it's "flappiness" in high winds, you may need to put a cord around your waist to hold it in place (there are ponchos that include a waist cord already).
Hope this helps.
Even breathable fabrics like Gore Tex will make you sweat when it's too warm - there needs to be a certain temperature difference for the fabric to work. So, you'll need to increase ventilation. The aforementioned pit zips are a good idea. A waterproof hat/cap instead of the jacket's hood also helps. Or just use an umbrella ...
I make sure the rain jackets I buy have pit zips. They make a big difference. I have also left the jacket at home and used compact umbrellas for hiking when I'm walking on open area paths. In some cases when I'm wearing a jacket I can stick the umbrella behind my head into the jacket and don't have to carry it with my arms. However, umbrellas can be a problem if you walk in woods with a lot of branches. I wish someone would make a decent long poncho. But, the ones I have seen are all too short and don't cover one's arms very well. The open sides would provide good ventilation.
All answers seem focusing on better outfit. But in rain, the air is completely saturated with water. Therefore your sweat is not going to evaporate. Not even with the most breathable or wicking fabric. If given enough time and assuming you keep sweating and it rains all day, any clothing you wear will saturate with your sweat. Some fabrics wick away your sweat and may feel a bit drier longer which helps just a little. And make sure that no rain is seeping into your suit somewhere.
As you mentioned yourself, the best way is to sweat less. Maybe walking slower or more relaxed?
I've bought lots of jackets from ebay and you can get some good gear. I have also picked up Goretex Active Jackets and the latest Endura jacket (more breathable than any Goretex-allegedly) It is interesting as I have put these jackets over steaming hot water and with a very bright torch, you can see the vapour pass through the material.
BUT with all these jackets, I can wet out in any weather. I have worn these jackets on dry days, wet days, cold and mild days. I will be pretty wet after a 35 mile bike ride in all conditions. I am a sweaty Boy!
Condensation may be an issue in rain or the cold. Jackets get cold from the outside and warm from underneath makes it sweat. Breathability also works both ways; dampness from outside can go from outside to inside jacket if the conditions are right, making the inside more damp; it's not a one way street. I've also not understood how you can be kept dry of you sweat and raise the inside humidity to 100% and if the outside humidity is 100% then where does your inside humidity go? I learned a membrane needs to have a difference from one side of the fabric to the other for airborne moisture to travel. If both sides are equal then nothing will travel whatever the breathability of the fabric. 80% humidity inside the jacket and 80% humidity on the outside and vapour will not travel as both sides are equal.
I think if a jacket has zips then it's really saying it doesn't work. Softshell is way better and lets the air through to change the damp air underneath. That changing of the air is key to keeping drier. I hoped the windproof/waterproof materials may cut down on the amount of layers but I'm back to layering up on cold days with semi windproof tops. The Endura Jacket is now for emergencies when I get caught out by a rogue shower. I don't ride in the rain now at all barring rougue showers. The radar app from Netweather is the best for seeing if I ride or not :)
I know if I ride in the rain then I'll be wet with or without any jacket :p
