What is the difference between waterproof and water repellent?

There have been an increasing amount of articles emerging, explaining the difference between waterproof and water repellent, so we thought it was time to add to the discussion and look closer at the definitions and differences between the two, with particular focus on footwear.

What is the difference between waterproof and water repellent?

Firstly, how are both defined?

• Waterproof: Impervious to water
• Water Repellent: Fabrics that have received a finish or coating that is not easily penetrated by water (Source: Oxford English Dictionary)

Let's look at what it means to be waterproof. Footwear that has a waterproof label or tag similar to the styles used for hiking and trail running, means they are impervious to water (or no liquid can pass through them). Which is great if you are caught out in the elements or passing through streams and you need to stay dry, but how does a shoe actually become waterproof and what are the restrictions to having this type of footwear?

For materials and products to be considered waterproof they need to meet specific criteria. This criteria includes the amount of water pressure (psi) they can withstand before leaking or an "mm/24 hours" rating which equals the amount of rainfall a fabric can withstand in a single day before water starts to leak through.

In footwear terms, to be considered waterproof they will most likely have a barrier or membrane built inside as well as fully sealed seams and stitching, designed to keep water out and ensure your feet stay dry. However, if water enters the shoe above the ankle collar or sweat builds up, then your feet still become wet with the water unable to get out.

Sealed seams and membranes may protect feet from becoming wet but as they are built within the internal structure of the shoe they do not offer the same waterproof protection to the outside material. This can result in the shoe becoming very wet and heavy, leading to reduced comfort for the wearer, particularly on long hikes or runs.

There are of course solutions to this, such as the choice of material used as well as treating the outer surface of the shoe with durable water repellents (DWR). DWRs are coatings applied at the factory stage to fabrics making them water repellent (not proof). This treatment alongside the membrane ensures that the shoe lives up to its waterproof claims. However, these treatments can affect the functionality of the material as well as losing their effectiveness over time and re-treatments are usually required in the form of further sprays. In addition, they are rarely applied to all the materials used in the construction of a shoe, resulting in water ingress points.

There is also the issue of breathability or how much air can penetrate the fabric whilst still allowing sweat vapor to evaporate. The video below demonstrates the effect a membrane can have on breathability:




As you can see, the fabric and membrane layer significantly restricts air flow, while the stand alone fabric has no restriction and lets the air flow freely. While only a demonstration, it highlights the hidden impact a membrane can have on comfort and temperature control.

To combat this there are breathable membranes available that allow moisture (sweat) to escape but these tend to be more expensive than their non-breathable alternatives and can still allow levels of moisture build up to occur during exercise.

So what about water repellent?

Misunderstanding of the term water repellent can lead to disappointment when testing out a product, as you can find your feet or other parts become wet. For example, if a fabric or product is classified as 'repellent' this means it will repel water but is not impervious to it, or put in another way, there is a level of water pressure it can withstand before leaks start to appear. This is not seen as a disadvantage as the materials used will readily allow air to pass through removing the hot microclimate next to the foot, providing comfort and restricting sweating and discomfort.

Similarly to waterproof products there are criteria that fabrics and textiles have to undergo in order to test their repellency and protection levels and thus be given an overall rating. The Bundesmann test is one way of measuring this.

The test simulates actual rain environments by pouring a continuous shower of water over the surface of fabrics at a height to simulate rain, while at the same time lightly abrading the reverse side. The abrading technique is designed to encourage the water to seep through the fabric whilst also simulating movements of the body when a garment is being worn. The amount of water that seeps through, in addition to the amount absorbed into the fabric is then measured and the fabric is given an efficiency rating based on performance. The higher the rating the more repellent the material is.

How does P2i's liquid repellent technology - ion-mask™ differ?

ion-mask™ is a liquid repellent technology, meaning that liquid can still penetrate materials which have a natural airflow. What makes ion-mask™ so unique compared to other repellent treatments such as DWRs is that it is applied to the fully constructed shoe (or product) resulting in complete protection without changing the look or feel. Meaning that functionality such as breathability is not impaired. Furthermore, ion-mask™ is also solvent-free resulting in minimal environmental impact.

 

You can find out more about our liquid repellent technology in the video below and by visiting the ion-mask™ page.