A Guide to Waterproofing – Principles, Practicalities, Performance

The science of modern waterproof apparel can seem impervious to easy understanding. This material or that? How important is this feature I keep reading about, and which names can I trust? What do the claimed figures actually mean, and does spending more buy better performance? Simply put, what really makes the difference I’ll feel?

And if we spend our spare time in nature because we love our planet and its most challenging climates, does our chosen equipment harm the environment or respect it?

Like most things in life, it comes down to a few core principles. Here’s our ground-up, field-ready, planet-aware guide, as short and informative as we can make it.

1. DRY FROM THE SKY BUT WET FROM SWEAT? BAD BET.

Mankind’s first attempts at waterproofed apparel focused on one aim: keep the elements at bay. From the first Inuit parka to Shackleton’s era of rubberised cotton, imperviousness proved relatively attainable. But as anyone who’s tried to climb a mountain in a ‘70s cagoule can attest, keeping liquid out is only half the task.

A fabric that doesn’t breathe will leave you damp from the inside after the first steep ascent. And being soaked in sweat as unhelpful to our wellbeing as a leaking seam, zip or neckline.

When we’re wet through, we’re not only miserable but also vulnerable. Sodden skin is colder skin, requiring more effort from inside to keep us alive – especially in the wind, and especially when active. In the extremes, it’s life or death. Closer to home, it’s the difference between “let’s push on” and “how far back to base?”

So we need to re-frame the task as moisture management. Here’s how.

2. THINK IN SYSTEMS

The answer lies in layers. If beating rain is the aim, the outer shell has no need to be warm. Windproof and waterproof is fine. Even snow and ice are best handled by a systemic approach.

A well-chosen base layer will wick moisture from the skin, absorbing it without feeling damp.
The right mid-layer will insulate from the outside climate while avoiding over-heating from within. As activity levels and temperatures rise, it will pack small and add minimal weight to your load.
The ideal outer shell will not only protect from the elements, but also allow moisture out - and ideally feature flexible ventilation to manage your internal micro-climate. When not required, it should be unobtrusive to carry and ready at a moment’s notice at the first hint of rain.

Shackleton can provide precisely what you need.

3. UNDERSTAND WHAT’S IN YOUR OUTER LAYER

Most serious modern waterproof jackets use a 3-layer construction:

Outer fabric for durability, often with an extra DWR coating;
Waterproof-breathable membrane for moisture management;
Inner liner for comfort.

Properly laminated together, these will keep you dry inside and out – provided the potential weak links are treated right. These tend to be seams and openings, so reassurance comes from phrases like “fully seam-sealed”, protected zip housings and thought-through closing mechanisms on the cuffs and neck.

All Shackleton waterproof shells feature all of the above.

The outer fabric will be tested to withstand the pressure points and wear that can limit efficacy over time. The Durable Water Repellent (DWR) outer coating is there so water droplets bead off instead of soaking in. Once the fabric wets out, breathability wanes - even if the membrane still works. So DWR is belt-and-braces when standing still, but critical when effort levels rise.

The middle membrane will be precision-engineered with microscopic pores too small to let in liquid, but large enough to let vapour escape.

The inner lining protects the membrane without affecting the breathability, as well as adding softness against the skin if wearing a short-sleeved base layer.

4. KNOW YOUR NUMBERS

A serious piece of storm-proof apparel will carry an HH rating for water resistance and a MVTR rating for breathability. Understanding these, and applying them to your expected use case, is critical to choosing well.

Waterproofing rating

HH stands for Hydrostatic Head, the test method used to describe the amount of water pressure a fabric can withstand.

Imagine a 30-metre tube sitting on top of a fabric’s surface, being slowly filled with water. The results are expressed as the height of the water column that the fabric can withstand before water is able to pass through, so 20,000mm equals a column 20m high. A modern Hydrostatic Head testing machine accurately simulates the same pressure.

5,000mm is around the lowest threshold for claiming ‘waterproof’, but can’t be relied on in a heavy shower.
10,000mm will protect you in high impact, heavy showers and downpours, and is effective in a wide range of conditions.
20,000mm will withstand high-pressure rain and the very worst weather.

Shackleton parkas require a 10,000mm (H/H) rating or above, though many have a 20,000mm (H/H) rating – the same as all our outer shells.

Breathability rating

MVTR (Moisture Vapour Transfer Rate) records the amount of evaporation through a square metre of fabric over a 24-hour period. To be sure it works as intended as the pulse level rises, look for a figure of 20,000 – as in our Quest hardshell jacket.

Breathability can also be measured as RET (Resistance to Evaporative Heat Transfer), where a lower number equals better performance. 20,000 MTVR is similar to a RET rating of 5.93 -exactly what our Markham hardshell attains.

5. INTERROGATE THE MATERIALS FOR SUSTAINABILITY CREDENTIALS

The first breathable/waterproof membranes used expanded PTFEs, long-chain chemical compounds that don’t break down and can’t be recycled. Over time they build up in the air and water systems, ultimately finding their way into the food chain, posing a threat to both wildlife and humans. These chemicals have been linked to immune system reduction and are also carcinogenic. No Shackleton fabrics use PTFEs.

A DWR can be similarly harmful, this time thanks to PFCs (perfluorocarbons, polyfluorocarbons and fluororesins), compound chain chemicals that share similar detrimental effects on the environment. Much time has been invested in the innovation of PFC-free (C0) DWR finishes which work just as well or better, without containing any harmful chemicals. While never the most economical choice, these are what Shackleton exclusively chooses to use.

6. EXAMINE FEATURES, CONSTRUCTION & FIT

Insist on:

Fully taped seams (non-negotiable)
Adjustable hood (preferably helmet-compatible)
High-quality zippers with storm flaps or water-resistant coating
A proper fit over your insulating layer, as close as you can without restricting movement or airflow

and ideally