How a waterproof jacket works: HH, MVTR, RET and layers

Choosing a waterproof jacket is not just about looking for a high waterproof rating. To understand how a garment will perform in the mountains, it is worth looking at how it is constructed, what membrane it uses, how much it resists water, and how it manages the vapor generated by the body.

How does a jacket become waterproof?

Modern waterproof garments use a very thin barrier that prevents water from entering from the outside while simultaneously allowing some of the moisture generated on the inside to be managed.

This barrier can be applied as a coating on a fabric or manufactured as a laminated membrane that is then bonded to the outer fabric. The type of membrane, the fabric, and the final construction determine a good portion of the jacket's weight, durability, and breathability.

2-layer, 2.5-layer, and 3-layer

2-layer

The membrane or coating is bonded to the outer fabric. It is a simple construction that can be lightweight, although it requires additional protection against abrasion when used in garments.

2.5-layer

Adds a very light print or protection on the inside of the membrane. It allows for reduced weight and volume and is common in compact garments where lightweight and packability are priorities.

3-layer

The membrane is sandwiched between an outer fabric and an inner fabric. This construction usually offers greater durability and protection, which is why it is common in jackets intended for demanding mountain use, mountaineering, and frequent use.

What does the water column or HH mean?

The water column or Hydrostatic Head (HH) measures the water pressure a fabric can withstand before water penetrates it. It is usually expressed in millimeters.

For example, when a technical sheet indicates 20,000 mm, that figure comes from a laboratory test of resistance to water pressure. It is important information, but it should not be analyzed in isolation: seam design, zippers, hood, and the overall construction also influence actual protection.

MVTR: the higher the better for vapor transfer

MVTR stands for Moisture Vapor Transfer Rate. It measures how much moisture vapor can pass through one square meter of fabric over 24 hours and is typically expressed in g/m²/24h.

• High MVTR = greater vapor transfer.
• Low MVTR = lower vapor transfer.

Rab uses this metric in numerous technical sheets. For example, several current models with Pertex® Shield publish HH and MVTR values to facilitate comparison.

RET: here a lower value is better

RET measures the fabric's resistance to evaporation. Unlike MVTR, the interpretation of RET is the opposite:

• Low RET = greater breathability.
• High RET = lower breathability.

MVTR and RET use different test methods, so it is not advisable to directly compare an MVTR figure with a RET figure.

What is the role of DWR?

The DWR (Durable Water Repellent) treatment helps the outer fabric repel water and take longer to saturate. It is not what makes the jacket waterproof on its own: that function belongs to the membrane or coating and the garment's construction.

When the outer fabric becomes saturated, the jacket may still be waterproof but feel colder and manage moisture more poorly. That is why maintenance and renewal of the repellent treatment are important.

Waterproofing is not the same as comfort

A jacket can have a very breathable membrane and still feel too warm for intense activity. Comfort also depends on the weight of the fabric, elasticity, fit, the layers you wear underneath, and ventilation elements like underarm zippers.

Which construction to choose

• Hiking and occasional use: a 2.5L can offer a good balance between protection, weight, and price.
• Demanding trekking and frequent mountain use: it is worth prioritizing durability, fit, and ventilation in addition to HH/MVTR figures.
• Mountaineering and severe conditions: a robust 3L construction is usually more suitable when abrasion and exposure are greater.

Explore Mountain Group's waterproof jackets

Men's waterproof jackets · Women's waterproof jackets

Content reviewed by Mountain Group based on technical documentation from Rab. For more information on breathability, you can consult the official Rab guide on MVTR and RET.