COMPARING PERFORMANCE
Out of all these different fabrics, which one is best? It’s hard to say. There are many variables, including climatic conditions, levels of activity and individual physiology, as well as what you’re wearing underneath your jacket. And while all jackets work pretty well when new, you may see a drop-off in performance a few months or a year down the line.
The fabric is also only one element of a waterproof jacket. That’s why taped or bonded seams, stormflaps and waterresistant zippers are important. Similarly, all jackets have a few critical potential failure points, namely four big holes – one at the end of each sleeve, one at the bottom and the one at the top that you stick your head through. Rain can seep through even the tiniest gap, so a hem drawcord, a decent hood and adjustable cuffs are vital, as is a good fit. Most brands do provide a couple of stats that can help compare the performance of different garments.
Hydrostatic head
The industry standard for measuring waterproofing is ‘hydrostatic head’. In a controlled test, a column of water is placed over an area of fabric. The height of the column (and therefore the water pressure) is increased until water seeps through. Results are expressed in millimetres. For outdoor kit, they range from 1500mm to 30,000mm. That’s 30 vertical metres of water bearing down on the fabric. Pack straps and hipbelts or contact with rocks and the ground all increase the external pressure on the fabric. It is often at these points of contact that moisture will seep through.
Moisture Vapour Transmission Rate (MVTR)
MVTR is one way to assess a fabric’s breathability. Again, these tests are done in a lab under controlled conditions. It measures the rate at which moisture permeates through a fabric, measured in grams per square metre per day.
For hillwalking waterproofs, MVTR figures typically range between 5000 and 35,000 – though more impressive figures can be achieved by changing the method by which garments are tested. As such, it’s difficult to objectively rely on MVTR figures.