A Guide to Technical Shells

Explore the basics of technical shells and learn why they play such a key part in rain protection so can find the piece of rainwear that’s perfect for you.

Someone stands in a raincoat with their back to the camera. Water is sitting in beads on their hood and the landscape in the background is forested.

Photo by Andy Køgl

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In this article, we will explore the basics of technical shells and learn why they play such a key part in rain protection. We’ll cover everything from the features that make them so versatile to the differences that make them each unique, and you’ll learn how to select a piece of rainwear that’s perfect for you!

What is a technical shell?

“Technical shell” is a term used to describe the outermost layer in a layering system, such as a windbreaker or a rain jacket, that helps protect against the elements. The technical shells we will be discussing in this article are not insulated, but rather are outer layers that go over existing insulation layers to help stop the wind chill, rain, or whatever else the weather may throw at you.

Why choose a shell over an insulated jacket?

The lack of insulation makes shells a more versatile layering piece of rain gear, compared with insulated outer jackets that may only be suitable when the weather is cold enough for them. Shells give you the flexibility to choose the insulation you wear underneath. This separation of insulation layers from the shell also keeps it more breathable than insulated jackets that have lots of layers of material — from the weather-proof outer layer to the insulation to the backing fabric. Not to mention, in the case of many insulated jackets, they do not have pit zips to vent out heat as many shells do.

This is not to say that insulated jackets don’t have a place in a closet, as they are very useful for those looking for a ski jacket or an urban winter jacket. However, for camping and hiking, shells provide the flexibility for year-round use.

What features do these shells include?

The feature set of a shell varies based on model, purpose, and brand, but we will break down the most common differences in features and explain what they mean.

Layers (L)

Commonly listed as 2L, 2.5L, or 3L, the “L” describes how many layers of material the jacket is made up of.

  • 2-Layer (2L): A 2L shell consists of two layers of fabric, with the outer fabric bonded to the waterproof membrane. There is no liner layer, so a loose liner such as mesh is typically used in less expensive shell jackets. This separate liner can increase weight but also improve next-to-skin comfort. These tend to be the cheapest rain shell options out there.
  • 2.5-Layer (2.5L): A 2.5L shell consists of two layers of fabric (outer fabric and waterproof membrane) and an inner “0.5L” of a spray or print-on protective coating. This helps with next-to-skin comfort and prevents oils and contaminants from degrading the performance of the waterproof membrane. These are typically the most common budget shell options and are very versatile due to their lightweight and packable nature.
  • 3-Layer (3L): A 3L shell consists of three layers of fabric — outer face fabric, waterproof membrane, and a liner layer. This is the most durable and protective shell fabric design. Typically, it is stiff and “crinkly,” making it trend bulkier than the other options. Three-layer shells are on the higher end of the price scale.
A graphic showing an image titled 2L with two fabric layers, an image titled 2.5L with three fabric layers, and an image titled 3L with three fabric layers.

A graphic comparison of 2L, 2.5L, and 3L shell fabrics. The circled 1 is outer face fabric, 2 is the waterproof membrane, 2.5 is the print or spray-on protective layer, and 3 is the backing/liner layer. Photo by Burton

Waterproof vs. Water-Resistant vs. Windproof

The naming of shell features can be very confusing! Typically, windproof shells and jackets are meant for emergency use due to their packability, or during activities in windy conditions where waterproofing isn’t needed. More on the waterproof membranes below!

  • Waterproof: fully protected from water.
  • Water-resistant: holds up against water, but not fully protected from it.
  • Windproof: usually doesn’t have a membrane to protect against water at all, but the fabric can stop the wind.

Waterproof Membrane:

The middle layer of a shell fabric lamination, the waterproof membrane, is where the waterproofing happens. Some popular membranes include GORE-TEX, eVent®, or The North Face’s® FUTURELIGHT™. Membranes are rated on a millimeter scale to determine how waterproof they are, as well as a breathability scale in grams per meter squared. These measurements are not usually directly listed, but they are a helpful gauge for choosing a suitable shell once you understand what they mean.

  • Waterproof Rating: Waterproof rating is measured in millimeters when a one-square-inch column is placed on top of the shell and water is continuously added — the resulting measurement relates to how high up the column of water gets before it leaks. Typical waterproof ratings are as follows:
    • 0 to 5,000: Water resistant, good for light rain or dry snow.
    • 5,000 to 10,000: Lightly waterproof, good for light-to-medium rain or snow.
    • 10,000 to 15,000: Waterproof, good for medium or constant rain or snow.
    • 15,000 and up: Very waterproof, good for heavy conditions.
  • Breathability Rating: The breathability rating is measured based on how many grams of water vapor can breathe through a square meter of material, or how much moisture can make it through the membrane. As a note, it’s strongly recommended to wear clothes that can wick moisture away from the skin underneath so that the shell can also help with its breathability. Typical breathability ratings are as follows:
    • 5,000 to 10,000: Less breathable and meant for less active activities, such as resort skiing or urban use.
    • 10,000 to 15,000: Breathable for many active uses, such as backcountry skiing and hiking.
    • 15,000 and up: Highly breathable for warmer weather or high exertion where sweating is common, such as trekking or hiking in the mountains.

Pit Zippers

Also known as “pit zips,” these are zippers at the armpit of the shell that you can open to vent out heat.

Storm vs. Drop Hood

A storm hood means the hood is connected to the collar of the jacket in one piece, while a drop hood means the hood and collar are separated.

A product image of the hood on the Arc’teryx Alpha AR shell.

This Arc’teryx Alpha AR shell features a storm hood. Photo by Arc’teryx

  • Storm Hood
    • Pros: It is more comfortable while the hood is worn up, the collar is usually easier to layer under, and the collar can go higher up the face for better protection from the elements.
    • Cons: The collar may pull toward your face and chin and be uncomfortable when the hood is down.
A product image of the hood on the Arc’teryx Beta AR.

The Arc’teryx Beta AR features a drop hood. Photo by Arc’teryx

  • Drop Hood
    • Pros: It is more comfortable while the hood is down and not being used.
    • Cons: The collar typically only goes up to the top of the neck and is less protective in the harshest conditions.

Helmet-Compatible Hood

Many hoods, especially those meant for alpine activities, can be worn with a helmet underneath, such as a climbing or ski helmet. Many brands will advertise this feature with their shells. Some companies use a reinforced brim to keep the structure of the hood up and make sure it doesn’t sag down in the rain. Even with helmet-compatible hoods, they are adjustable to fit your head (usually with a releasable drawstring) so you don’t have a huge hood flapping in the weather.

A product image of a male model wearing a Mammut Kento Jacket with a helmet under it.

This is a helmet-compatible hood on the Mammut Kento Jacket. Photo by Mammut

Trim vs. Regular Cut

Depending on the brand, model, and intended use of the shell, its cut may be trim or regular. A regular cut gives space underneath to layer with fleeces, while a trim cut might be more suited to warmer weather where fewer layers will be worn underneath.

Durable Water Repellent (DWR)

DWR is a coating applied to the outer or face fabric that helps repel water and bead it off the surface. This coating may need reapplying in the long term and also when shells are put into the dryer.

  • Even if the DWR is wearing away and water stops beading from the surface — what we call “wetting out” — the waterproof membrane will still do its job to keep water out.
  • Re-treating can be done using various laundry products to refresh or recoat the DWR.

Hem Length

Make note of the hem length of your shell because some hem lengths are cut longer for better climbing harness compatibility.


One feature that is quite important to notice is if the pockets are hip belt compatible. This helps keep the pockets out of the way of the backpack’s hip belts or climbing harnesses so you can reach your items in the hand pockets. Some shells have different configurations of hand and chest pockets, and some even have arm pockets — that skiers can use with their ski passes, for example — so keep that in mind.

Adjustable Cuffs

Some cheaper shells may have elastic cuffs, but adjustable cuffs made with Velcro make it easy to tighten or loosen the cuffs however you see fit.


Nowadays, most seams are taped from the inside.


Sometimes, special shells will use two-way zippers so you can unzip the bottom for more freedom of movement near the hip and legs. The way the zippers are waterproofed can also reflect on the quality of the gear.

  • Waterproof Zippers: These have coatings on the outside of the teeth to keep them waterproof. It’s a more elegant solution that is featured on most shells nowadays.
  • Zippers with Storm Flaps: The storm flap covers the front of the zipper with Velcro or snap buttons to keep it closed, or will cover the back to prevent water from getting past the zipper.

Final Thoughts

Here are a few final considerations when choosing the right technical shell for you:

  • High-visibility gear can really help with search attempts since more neutral tones can blend in with nature!
  • The packability of a shell depends on its fabric and the membrane used (a combination of outer fabric, membrane, and layer count). For example, a 2.5L shell with a light outer fabric and less waterproof membrane is more packable than a heavy-duty, 3L, GORE-TEX Pro shell that is meant to withstand all conditions.
  • Many times, there isn’t a need to go completely overboard with the waterproofing of a shell (think full GORE-TEX Pro on a rain jacket you’ll only wear around town). You can save money by choosing something that best suits your needs (in the earlier example, a more packable and lighter shell will do the trick).

In conclusion, technical shells are an incredibly useful piece of gear that everyone should have in their closet. We all have different use cases for our shells and various budgets to meet as well, so many of the factors and features above should be taken into consideration when finding the shell that best suits you.

If you have any questions regarding shells and how to choose one, or are already looking at a few and want help making a final decision, feel free to talk to a camping and hiking expert at Curated!

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Written By
Hi! I'm Howard. I'm an electrical engineering student and the president of the University of Connecticut Outing Club. I got into the outdoors a few years back through UConn Outing Club and have since been living to enjoy the outdoors. I love to hike, camp, bike (road, gravel, or moutain), and snowbo...

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