arcteryx and patagonia

At the bottom of this post, find my blueprints and complete guides to best Arc'teryx jackets and best Patagonia jackets.

Overview

The advantages Nano Puff has over Atom LT is that it:

• Is more weather resistant,
• Comes with and stuffs into its own sack (Atom LT doesn't come with one),
• Is slightly lighter {363 grams (12.8 ounces) vs 415 grams (14.6 ounces)}

Now you understand why Nano Puff is a really popular jacket around traveler folks, and also why it's one of my top synthetic insulated jacket for travelers.

Atom LT, on the other hand,

• Is much more breathable (because of its famous side fleece panels), 
• Is more comfortable,
• And looks better (at least to me - especially this Orion color with Flux interior). 

So, in summary, if you'll be using the jacket both in the town & during high output activities, then your jacket is probably Atom LT (if, for some reason, Proton LT isn't an option for you). If you'll mostly be traveling with the jacket and won't be physically active with it, then Nano Puff would probably be a better choice.

Lastly, do not get either of these jackets if you'll be out in below 30 deg F (0 deg C) a fair amount of days - because you'll quite likely to feel chilly inside them (assuming no substantial under layering - just a long sleeved shirt) unless you run much warmer than the average person.

Different insulation materials

Atom LT's Coreloft is made with highly crimped multi-denier siliconized polyester yarn. Its lightweight, breathable and thermally efficient 100% polyester staple fiber is compressible and has good loft retention. Comes in the following six weights:

1. 1.2 oz/yd2, 40 g/m2,
2. 1.8 oz/yd2, 60 g/m2 (the density Atom LT uses),
3. 2.4 oz/yd2, 80 g/m2,
4. 3.0 oz/yd2, 100 g/m2,
5. 3.5 oz/yd2, 120 g/m2,
6. 4.2 oz/yd2, 140 g/m2.

So how do these different insulation techniques play out when using these jackets? 

Breathability

Atom LT's 60 g/m2 is the higher breathability / less warmth region for Arc'teryx's jackets. 60 g/m2 also compromises weather resistance to achieve more stretch and comfort.

The main advantage you'll have with the Nano Puff's 60 grams of Primaloft Gold Insulation Eco over Atom LT's 60 g/m2 Coreloft, on the other hand, is that it's more compressible (which is why it comes with a stuff sack) and provides superior wet-weather performance.

Atom LT's side fleece panels

The game-changer here is actually Atom LT's side fleece panels.

If you're having a dilemma between these two jackets, then you should have heard of these panels before already - they're admired by many users.

First I want to say that using fleece panels with the intention to make a jacket more breathable is considered outdated in today's outdoor gear world. 

The reason is that there has been a lot of advanced breathable insulators released into the market. Jackets made with genuinely breathable materials such as Arcteryx's Proton LT and Patagonia's Nano Air started to take the lead.

But there are many climbers and skiers still using jackets with side fleece panels today. My, too, first choice would be Proton LT as you can see here when it comes to choosing a jacket for a combination of casual and active use - but Atom LT is a good alternative.

Needless to say, Nano Puff doesn't offer side fleece panels.

Warmth

I'd say, generally speaking, when it's dry out, with only a long sleeved shirt under and without a shell on top, with a mild wind and very low to no activity level...

The approximate lowest temperatures an average person can wear these jackets without feeling cold would be around 30 deg F (0 deg C).

Like I said earlier, they provide about the same warmth as you see. If you think you run hotter or colder than the average person, then shift this temperature {30 deg F (0 deg C)} accordingly.

When there's anything more than a light rain, though, Atom LT's performance will drop slightly below Nano Puff's.

Which brings me to my next point...

Different face fabrics

This factor will play out in durability, comfort and weather resistance. 

Although side fleece panels of LT make it much more breathable, it inevitably compromises wind resistance in return significantly. Wind will cut right through it. 

You can solve this by under layering an Atom LT with a wind-shirt. But that requires extra effort from the buyer's side, so I'd write minus points for Atom LT in this department.

The fabric of Nano Puff (Shell: 1.4-oz 20D 100% recycled polyester, Lining: 1.3-oz 22D 100% recycled polyester) isn't any better than that of Atom LT (Tyono 20D / Polartec Power Stretch), but it isn't equipped with side fleece panels, it certainly isn't THAT vulnerable against strong winds. 

Both are DWR coated.

Gentle, smooth, stretchy inner surface of Atom LT provides much more comfort than Nano Puff. This is especially important when you're active with the jacket.

Slightly more robust outer shell of Nano Puff is slightly more durable than Atom LT's stretching fabrics which is intended to increase comfort during high output activities.

But still, the Nano Puff won't be able to counter an abrasion caused by a stiff or pointy rock when climbing either, just like Atom LT. I wouldn't say they're much different than one another when it comes to durability.

Conclusion

So, in summary, if you'll be using the jacket both in the town & during high output activities, then your jacket is probably Atom LT (if, for some reason, Proton LT isn't an option for you). If you'll mostly be traveling with the jacket and won't be physically active with it, then Nano Puff would probably be a better choice.

I'd recommend both products WITH the hoody. 

We'll get to compare the Proton LT vs Nano Air and Atom LT vs Nano Air. 

In terms of warmth, all three are the same. But what about other departments?

But first, you'd probably better go ahead and read the foreword of my Atom LT vs Proton LT article. I lay out some important facts about the Arcteryx's motivation behind launching Proton LT there. 

If you don't have time, then let me summarize the part that concerns you: 

1. Atom LT started to lose its share when the advanced fabrics and insulation pieces were released into the market (such as Patagonia's Nano Air). 
2. Arcteryx's response against these higher technologies was to release a superior replacement to the Atom LT. And that was Proton LT. 

This information is important for this comparison because it might be wiser to compare the Nano Air to the Proton LT instead of the Atom LT.

Packing

Air is packable whereas the Atom and Proton LT aren't. 

The differences are:

Breathability

This makes up the single biggest downside of Atom LT.

Perfectly breathing FullRange insulation prevents you from overheating during any high output activity.

Atom LT, on the other hand, was released years before the Nano Air. So it isn't equipped with one of those advanced breathable active insulation pieces.

That's why its insulation can't keep up with the breathability of the cutting-edge jackets such as Nano Air or Proton LT. 

But Atom LT comes with a well-known feature: Side fleece panels. Thanks to these panels under the arms, air can circulate much more and keeps you less sweaty when you're physically active.

This helps the Atom LT with its breathability, but undoubtedly not as much as that of the other two. 

Also, all these jackets are DWR coated. 

Warmth & Weather Resistance

Side fleece panels of Atom LT become a disadvantage when it's cold, windy and/or rainy. They'll let some foul weather in. 

However, in spite of these notable disadvantages, Atom LT still stays slightly warmer than the Nano Air because of the Air's somewhat "fragile" construction. 

Absence of any side fleece panels simply doesn't cut it for Air in this manner. 

In terms of warmth, Proton LT is positioned somewhere in between. 

When it comes to weather resistance, on the other hand, relatively outdated outer fabric of Atom LT holds it back. Like Atom LT, Nano Air is also held back, but by its highly breathable face. 

Proton LT seems to have found the sweet spot, and performs noticeably better than each of them. 

Conclusion

In short:

• Getting the Nano Air (2019 version) would probably be a better decision if you're looking for an athletic piece to be used for high output activities ONLY.
• If you're going to use it in the neighborhood when it's cold out as well, then I'd recommend the Atom LT - but I'd also consider getting Proton LT as well (so read on).
• You can look at Proton LT as a more durable, comfortable and weather resistant but less breathable alternative to the Nano Air. If you'll be using the jacket both in the town when it's cold out AND during high output activities, Proton LT can really be one of your best choices.