Why Do I Still Get Wet in My Waterproof, Breathable Rain Suit?

Just because you’re getting wet in your rain gear does not mean it’s ineffective. Here are some reasons, and solutions, for your rain gear selection process.

• By Brian Nutt
• Jun 01, 2020

Basic question, right? I bought a rain suit to stay dry. I even spent the extra money to get one that is breathable, but sometimes, somehow, I still get wet. Is the rain suit leaking? Should I send it back? What is going on? These are common issues with rain wear, and they happen whether the rain wear is breathable or not.

Before we get started, please keep in mind we are not talking about liquid chemical protection here—just rain. Most breathable products are not intended for chemical protection, but some are, so make sure you check with the manufacturer.

Understanding Breathability. First, it is important to understand what makes rain suits breathable. The most common method is to use a coating or laminate comprised of polyurethane or ePTFE (expanded Polytetrafluoroethylene) on the product that will keep large droplets of water out but also allow microscopic droplets to pass through. This process is referred to as Moisture Vapor Transmission (MVT).

How does this work; can it also come in from the outside? Well, maybe if you are wearing the suit in a 100-degree rainstorm, but probably not. The coating allows water vapor to pass from the hot humid side (the interior of the suit close to the wearer), out to the cooler (exterior side). If you were to wear it in an environment that was hotter and more humid on the outside than the inside, the moisture could pass the other way. However, under those circumstances, you would be sweating so much it would not make sense to wear the rain suit at all.

Moisture Collection. Now that you understand a bit about how a breathable fabric works, here is how and why you can still get wet. The quick explanation is you are sweating too much or outworking the capacity of the coating to vent the moisture you are emitting. However, the answer could be a lot more than that. If you are sweating at all without the suit on, you are going to continue and probably even perspire more with it on. No matter how breathable the fabric is, some of, and maybe a lot of, that moisture will collect. Just like working in a t-shirt on a hot day, there is no rain and no rain suit, but your shirt is wet. Again, the rule of thumb is that if you are already sweating before you put it on, plan on sweating more while you wear it.

Not only is your body emitting moisture, but it is also heating up the interior of the suit and creating a temperature differential that can cause condensation to form on the inside of the suit. Think of a cold drink in the summer and all the moisture that collects on the outside of the glass (condensation). It is not because the glass is leaking, but rather that the glass is cooler and causes the humid air to collect on the surface as water droplets.

The same thing can happen in any rain suit, breathable or not. Often times it is noticeable on a sweatshirt layered under a suit in the cold; the shoulders and back of the sweatshirt get damp because moisture is collecting on the inside and the sweatshirt is touching the suit in those locations and absorbing the moisture.

This does not mean a suit can never leak; when suits get older or have not been properly cared for, the coating can start to separate. You should be able to see that and know the suit needs to be replaced. You may notice the coating flaking or peeling off the fabric. This can be a bigger problem on a breathable rain suit than a non-breathable one. Remember, a breathable coating is passing moisture through it from the warm side to the cooler side.

But what happens if that fabric is soaking in water to clean off some dirt? When it is soaking, the environment is the same on both sides of the fabric, so the coating cannot pass moisture from one side to the other and it absorbs the water and begins to swell. If the coating swells enough, that will cause it to separate from the fabric itself. This means that breathable products are not going to have a long life if they must be laundered or soaked with much frequency. It is important to consider the application before you purchase any suit.

Condition. This being said, if a suit is in good shape, most failures will be very minor and will not allow much water to seep in. If you are getting very wet, it is most likely from the perspiration that your body emits or condensation collecting on the interior of the suit. If this is an issue you have experienced many times in the past, there are options available for you.

Many manufacturers offer products with an outer shell fabric that is waterproof with a coating on the inside and another layer of mesh or taffeta to line the suit and sit against your skin. This creates a buffer and allows for more airflow so that you do not feel the moisture inside the suit as much. Some manufacturers go a step further and offer removable liners that can be zipped in and out to add additional flexibility and comfort depending on the season or environment.

Another factor to keep in mind for products that have the coating on the inside is a treatment on the exterior of the fabric called DWR, or Durable Water Repellency. This is not what makes the suit waterproof, but it does help moisture to run off and not absorb into the fabric. Durable Water Repellency is a treatment that is normally applied when the fabric is made but will wear off over time with use and laundering. Purchasing a DWR spray or wash treatment can help to restore some of the properties and make the exterior of the fabric more water and stain repellant.

Unfortunately, there is no perfect rain suit; many are designed for specific climates or applications, and at a wide array of price points. If it is hot enough, it may not even be worth wearing one at all. But like everything else, if you do your research and choose a quality manufacturer you should be able to find a rain suit to fit your needs that will last you a long time.

This article originally appeared in the June 2020 issue of Occupational Health & Safety.