During sustained rain or drizzle, your perspiration accumulates on the inside side of your rain clothes and will gradually soak your inner layers. It doesn’t matter if your rain gear is made out of Gore-Tex, eVent, Tyvek, Nylon or some other breathable membrane, all rain gear will wet out, sooner or later.
Since you'll get wet after a while, prepare to stay comfortable anyway. The key is to wear clothing that feels good both wet or dry, so you can cope with any situation.
A wicking layer next to your skin and a softshell or fleece to soak up any moisture will keep you warm. A lightweight windproof top and pants protect you from rain and wind chill.
Any of these layers can be worn on their own depending on the weather and what activity you enjoy.
Around camp or home you just wear the base layer, maybe the fleece.
When swimming, wear the base layer or the windproof top and pants, or both.
Keeping warm is more important than keeping dry. If your rain gear starts to wet out and your clothes get soaked, you run the risk of getting chilled or even hypothermic in cooler weather conditions.
Wear additional base and mid-layers which may eventually get soaked, but help you keep more body heat. They will also reduce the transfer of cold from the surface of your rain clothes to your skin. Aim to keep the layer against your skin fairly dry and move moisture away from your skin.
Hike faster, eat and drink to keep you core temperature up. Dehydration can accelerate the onset of hypothermia, so keep drinking even if you don’t feel thirsty.
Next time you feel like the urge to buy a jacket made with the latest breathable fabric technology, remember that low tech solutions like layering, or arm pit/torso zips are more effective and cost far less.
There is a reason why jackets with pit zips and pants with side zippers remain so popular after being on the market for so long: mechanical venting works and it is far less expensive than high-tech fabrics. Pit zips are underrated in this era of breathable, waterproof garments.
If you can’t stay warm, set up a shelter and get into your sleeping bag to warm up until it stops raining. Wiggy's have a sleeping bags said to keep you warm even when soaking wet. You get into the sleeping bag wearing your wet base layer clothes and it wicks moisture away while you sleep.
Under high humidity conditions a wet out is difficult to avoid.
Even ventilation gives little help.
When you get soaking wet on your adventures, maybe it's time to take a bath.