A GUIDE TO HYDROSTATIC HEAD RATINGS

WHAT IS A HYDROSTATIC HEAD RATING?

Hydrostatic Head Rating is a measure of how waterproof a certain fabric is, this indicates the amount of pressure the material can withstand before it starts to leak through. This test is measured in millimetres (MM) which refers to the height of a column of water that the fabric can resist. Fabrics which have higher rating are suited for extreme weather conditions, the lower ratings are more suited for calmer conditions.

HOW IS THIS TEST CONDUCTED?

Test Preparation

• A section of the jacket’s fabric is taken and place onto the Hydrostatic Pressure machine

• The sample fabric needs to be properly secured to prevent any leaks.

Application of Water Pressure

• Water is then applied to the face side of the fabric at a controlled rate with either a column of water or using a pressurised chamber that applies force in Millimetres of water column.

• The pressure of water increases gradually until water seeps through the fabric.

Measuring water penetration

• This test continues until three drops of water appear on underside of the fabric.

• The pressure at this moment is recorded as the hydrostatic head rating.

An example of this is, if water starts seeping through at 10,000mm, the fabric will then be rated at 10,00mm waterproof.

INDUSTRY STANDARDS

In the UK, waterproof workwear must meet BS EN 343 Standards, this is ensuring the safety of workers exposed to rain.

The BS EN 343 Standard is the UK specific standard for waterproof Garments, covering both water penetration resistance and breathability.

WHAT ARE THE BENEFITS OF HYDROSTATIC HEAD RATINGS?

Weather protection: Higher hydrostatic head ratings offer better resistance against challenging weather, to ensure you are kept dry and warm whilst working.

Comfort and performance: When working in rainy conditions, it is important to be in clothing that provides comfort and keeps you dry. Jackets with higher head ratings provide this for you; they prevent discomfort, stop you from feeling the colder weather, and ultimately prevent hypothermia.

Breathability: The breathability of a jacket is dependent on the membrane/lamination used.

Increased longevity: High-quality waterproof materials last longer, which reduces the need for frequently replacing jackets.

THE DRAWBACKS

A jacket with a high hydrostatic head rating is useful, but if the seams, zippers, and waterproof coatings aren’t properly designed, water can still seep through.

Materials: There are a lot of lightweight fabrics on the market that produce very high results for waterproof and breathability. The waterproofness comes from the type of membrane/lamination used on the reverse of the fabric as well as the DWR (Durable Water Repellence) applied on the face of the fabric.

Higher cost: Waterproof items with higher ratings tend to be on the expensive side due to the advanced materials and coatings used in the making of the jacket.

WHAT IS THE RECOMMENDED HEAD RATING?

When it comes to choosing the right rain jacket or waterproof trousers there is many different factors to consider.

If you are looking for a heavy-duty HI-VIS garment which has minimal chance of rain seeping through and is suitable for extreme weather conditions, you need to look at a garment with a rating of between 10,000mm – 15,000m with taping applied to the seams.

If you are wanting a more lightweight, breathable garment but keeps you dry in rainy conditions, you would be looking at a rating of 5,000mm – 10,00mm. This is where ROKWEAR comes in. ROKWEAR offers a range HI IVS Jackets & Trousers that have Hydrostatic ratings from 5500mm to 6000mm as well as strong EN388 ratings. The Milford, Selborne, Witley and Blackmoor are a excellent companion when dealing with heavy rain and general outdoor work.