In FW23, Arc'teryx changed the naming scheme of women's counterparts. Women's Atom AR Hoody is now Women's Atom Heavyweight Hoody and Women's Atom LT Hoody is now Women's Atom Hoody. 

This change remains limited to the names though. The products remain identical. 

Atom AR is much warmer, weather resistant and durable than Atom LT. It's probably the best synthetic insulated jacket out there for stationary use under damp and cold conditions. Atom LT, on the other hand, is much more breathable than the Atom AR and is a fantastic jacket for high output activities. 

Links: 

Both are fantastic jackets that won't disappoint. 

Also read: 

You can also see this on Arc'teryx's own Naming Scheme Page here, for both Atom AR and the LT. Latest on the blog:17 Aug 2023: Arc’teryx FW24 is rolling out: First look4 July 2023: Best synthetic insulated jackets12 June 2023: Arc’teryx colors: Most and least liked (poll results)13 Mar 2023: I've been to Pfander and floodplain forests with my Nuclei SV13 Dec 2022: Arc'teryx Alpha Parka Review: The most impressive jacket of all time8 Dec 2022: Arc'teryx ReGEAR: OutdoorCrunch exclusive promo code!7 Nov 2022: 2023 Thorium Hoody is in - as well as the new Thorium Parka (yes, parka)2 Nov 2022: Beta Insulated Jacket: Pit zips AND two way zipper!7 October 2022: Proton Hybrid Hoody is live! The ultimate do it all?5 October 2022: DropHood vs StormHood: Pros/cons and best uses5 September 2022: Reviewing Arc'teryx Fall Winter 22/23 Gear5 August 2022: 5 things all Arc'teryx newbies should know#A sidenote here: Arc'teryx's PDF guide to jackets is GOOOLLLLDDDDD. Absolutely check that out too if you're interested in buying one. 

Going from top to bottom (Atom SL, LT and AR respectively), the warmth increases and the breathability decreases. 

All the differences between these jackets can simply be listed as follows: 

We'll get to the details and determine how MUCH one is better than the other in terms of each and every one of these differences - but you should know that for most of you the answer to it wouldn't be that important. 

Because it's like comparing apples and oranges. The purpose of these jackets are completely different and this should be your main focus. Keep that in mind as you read on. 

Arc'teryx Jackets: Temperature Ratings

NameEst. Temp (F/C)ReviewPit venting?Stuffs into itself?Two way zipper?TypeFill PowerFill Weight (grams)Fill Volume (FP x FW)Synthetic Insulator (SI)SI AmountFace FabricActivityFitWeightLength (CB) Arc'teryx Alpha (Men's - Women's)-18/-28ReviewNoYesYesDown850296251,600Coreloft90 g/m²N30r 2L GoreTex InfiniumClimbingRegular805 g / 1 lb 12.4 oz86 cm / 34 in Feathered Friends Khumbu-17/-27NoYesNoDown900378340,200Primaloft Gold200 gPretex Shield XTAll RoundRegular960 g / 2 lb 2 oz? Arc'teryx Ceres SV (Men's - Women's)-15/-26ReviewNoYesYesDown850240204,000Coreloft?Arato 30All RoundRegular880 g / 1 lb 15 oz86 cm / 34 in Mountain Equipment K7 (Men's)-13/-25NoYesYesDown800300240,000N/AN/A30D DriliteAll RoundRegular820 g / 1 lb 13 oz76 cm / 30 in Rab Positron Pro (Men's)-13/-25NoYesYesDown800300240,000N/AN/A40D Pertex Quantum ProAll RoundRegular740 g / 1 lb 10 oz85 cm / 33.5 in Arc'teryx Therme SV (Men's)-11/-24ReviewNoNoYesParka750211158,250Coreloft60 g/m²2L Gore-TexAround TownRegular1.072 kg / 2 lb 5.8 oz96 cm / 37.75 in Patagonia Grade VII (Men's)-11/-24NoNoYesDown800335268,000N/AN/A1.2 oz 15 & 20D Perfex QuantumAround TownRegular743 g / 1 lb 10.1 oz83 cm / 32.5 in Arc'teryx Firebee AR (Men's - Women's)-10/-23ReviewNoYesYesDown800225180,000N/AN/AArato 7 & 10All RoundRegular680 g / 1 lb 8 oz79 cm / 31 in Mountain Equipment Exo (Men's)-10/-23NoYesYesDown800265212,000N/AN/ANylonAll RoundRegular770 g / 1 lb 11.2 oz79 cm / 31 in Arc'teryx Thorsen (Men's)-7/-22ReviewNoNoYesParka750192144,000Coreloft60 g/m²90D 2L Gore-TexAround TownRegular1.1 kg / 2 lb 5.4 oz91 cm / 36 in Patagonia Frozen Range (Men's - Women's)-6/-21ReviewNoNoNoParka700268187,600N/AN/A4 oz 75-denier polyesterAround TownRegular1.253 kg / 2 lb 12.2 oz84 cm / 33 in Mountain Equipment Li. Ec. (Men's - Women's)-5/-20NoNoYesDown700295206,500N/AN/A50D DriliteAll RoundRegular822 g / 1 lb 13 oz72 cm / 28 in Arc'teryx Patera Long (Women's)-2/-19NoNoYesParka7507455,500Coreloft60 + 80 g/m²2L Gore-TexAround TownRegular1.1 kg / 2 lb 6.8 oz117.5 cm / 46.25 in Rab Neutrino Pro (Men's - Women's)-2/-19NoYesYesDown800212169,600N/AN/A20D Pertex Quantum ProAll RoundRegular585 g / 1 lb 8.6 oz77 cm / 30.3 in Arc'teryx Dually Belay (Men's)0/-18ReviewNoYesYesSyntheticN/AN/AN/AThermaTek92 g/m²30D NylonAround TownRegular705 g / 1 lb 9 oz84 cm / 33 in Arc'teryx Centrale (Women's)0/-18ReviewNoNoYesParka750157117,750Coreloft60 g/m²N90p NylonAround TownRegular885 g / 1 lb 15.2 oz95 cm / 37.5 in Arc'teryx Camosun (Men's)0/-18ReviewNoNoNoParka75010578,750Coreloft140 g/m²N150p-X Gore-TexAround TownTrim960 g / 2 lb 1.9 oz80 cm / 31.5 in Arc'teryx Cerium SV (Men's)0/-18ReviewNoYesNoDown850162137,700Coreloft80 + 140 g/m²Arato 7 & 10All RoundRegular415 g / 14.6 oz69.5 cm / 27.4 in Arc'teryx Revet (Men's)2/-17NoNoYesParka750?N/AN/A20d nylon/spandex double weaveAround TownRegular755 g / 1 lb 10.6 oz91 cm / 36 in Arc'teryx Piedmont (Men's)3/-16NoYesYesParka750218163,500N/AN/AArato 10Around TownRegular515 g / 1 lb 2.2 oz82 cm / 32.25 in Arc'teryx Fission SV (Men's - Women's)3/-16ReviewNoNoYesSyntheticN/AN/AN/ACoreloft Continuous90 + 65 g/m²N80p-X Gore-Tex 2LAll RoundRegular890 g / 1 lb 15.4 oz81 cm / 31.8 in Arc'teryx Alpha Lightweight (Men's)3/-16NoYesYesDown85011799,450Coreloft Compact40 g/m²Hadron 2L Gore-Tex InfiniumClimbingRegular540 g / 1 lb 3 oz? Outdoor Research Sup. Alp. (Men's - Women's)3/-16NoNoYesDown800182145,600N/AN/A30D Pertex Quantum ProAll RoundRegular825 g / 1 lb 13.1 oz85 cm / 33.5 in Arc'teryx Alessa Long (Women's)3/-16NoNoNoParkaN/AN/AN/ACoreloft80 + 120 g/m²N90p 2L Gore-TexAround TownRegular1.015 kg / 2 lb 3.8 oz123 cm / 48.5 in Patagonia Tres 3-in-1 (Men's - Women's)3/-16ReviewNoNoNoParka70011882,600N/AN/A5.5 oz polyesterAround TownRegular1.307 kg / 2 lb 14.1 oz85 cm / 33.5 in Arc'teryx Radsten Parka (Men's)3/-16NoNoNoParkaN/AN/AN/ACoreloft Compact120 g/m²NP100d Gore-Tex 2LAround TownRegular745 g / 1 lb 10.3 oz82 cm / 32.25 in Rab Electron Pro (Men's - Women's)5/-15NoYesYesDown800180144,000N/AN/A20D Pertex Quantum ProAll RoundRegular525 g / 1 lb 2.5 oz74 cm / 29 in Arc'teryx Therme Parka (Men's)5/-15ReviewNoNoYesParka75012090,000Coreloft60 + 80 g/m²P75d PolyesterAround TownRegular991 g / 2 lb 3 oz85 cm / 33.5 in Arc'teryx Macai (Men's)5/-15ReviewYes, zipsNoNoDown7506951,750Coreloft Compact60 + 100 g/m²N40p-X 3L Gore-TexSki/SnowboardRegular1 kg / 2 lb 4 oz76 cm / 30 in Arc'teryx Nuclei SV (Men's)5/-15ReviewNoYesYesSyntheticN/AN/AN/ACoreloft Continuous180 g/m2 + 90 g/m2Arato 15ClimbingRegular600 g / 1 lb 5.2 oz81 cm / 31.8 in Patagonia DAS Parka (Men's)5/-15NoYesYesParkaN/AN/AN/APrimaLoft Gold Insulation Eco133 + 40 gPertex Quantum ProAround TownRegular555 g / 1lb 3.6 oz84 cm / 33 in Arc'teryx Patera (Women's)5/-15ReviewNoNoYesParka7505843,500Coreloft60 + 80 g/m²2L Gore-TexAround TownTrim867 g / 1 lb 14.6 oz99 cm / 39 in Black Diamond Access Down (Men's - Women's)7/-14NoYesYesDown700155108,500N/AN/A30D ripstop nylonAll RoundRegular442 g / 15.6 oz76 cm / 29.75 in Arc'teryx Kappa (Men's)7/-14ReviewNoNoYesSyntheticN/AN/AN/ACoreloft Continuous140 g/m²N70p Gore ThermiumAll RoundRegular755 g / 1 lb 10.6 oz80 cm / 31.5 in Arc'teryx Prema Down Coat (Women's)7/-14NoNoYesParka7509269,000N/AN/ANylonAround TownRegular794 g / 1 lb 12 oz117 cm / 46.1 in Arc'teryx Radsten Insulated (Men's)7/-14NoNoNoParkaN/AN/AN/ACoreloft Compact120 g/m²NP100d Gore-Tex 2LAround TownRegular715 g / 1 lb 9.2 oz73 cm / 28.75 in Rab Microlight Alpine (Men's - Women's)7/-14NoYesNoDown700153107,100N/AN/A30D Pertex QuantumAll RoundRegular466 g / 1 lb 0.5 oz72 cm / 28.5 in Arc'teryx Thorium (Men's - Women's)7/-14ReviewNoYesYesDown750140105,000Coreloft80 + 140 g/m²Arato 30All RoundRegular517 g / 1 lb 2.2 oz71.5 cm / 28.1 in Feathered Friends Eos8/-13NoYesNoDown90010594,500N/AN/APertex QuantumAll RoundRegular306 g / 10.8 oz? Arc'teryx Thorium AR (Men's - Women's)8/-13ReviewNoYesNoDown75013097,500Coreloft80 + 140 g/m²Arato 30All RoundRegular490 g / 1 lb 1.3 oz72 cm / 28.3 in Patagonia Macro Puff (Men's - Women's)8/-13ReviewNoNoNoSyntheticN/AN/AN/APlumaFill135 + 90 g10D Recycled nylon ripstopAll RoundRegular435 g / 15.3 oz79 cm / 31 in Arc'teryx Macai LT (Men's)8/-13Yes, zipsNoNoDown7504936,750Coreloft Compact60 g/m²N40p-X 3L Gore-TexSki/SnowboardRegular855 g / 1 lb 14.2 oz74 cm / 29.1 in Arc'teryx Seyla (Women's)8/-13NoNoYesParka7509269,000N/AN/AArato 10Around TownRegular507 g / 1 lb. 1.9 oz.87 cm / 34.4 in Patagonia Fitz Roy (Men's - Women's)8/-13NoYesNoDown800128102,400N/AN/A20D NylonAll RoundRegular632 g / 1lb 6.3 oz74 cm / 29 in Arc'teryx Koda (Men's)8/-13NoNoNoParkaN/AN/AN/ACoreloft80 + 140 g/m²N80p-X Gore-TexAround TownRegular720 g / 1 lb 9.4 oz75 cm / 29.5 in Patagonia Vosque 3-in-1 (Women's)10/-12ReviewNoNoNoParkaN/AN/AN/AThermoLite100 g65% nylon, 35% polyesterAround TownRegular1.360 kg / 3 lb90 cm / 35.5 in Patagonia City Storm Down (Men's - Women's)12/-11NoYesNoParka700191133,700N/AN/A4.2 oz polyesterAll RoundRegular468 g / 16.5 oz91 cm / 36 in Patagonia Jackson Glacier (Men's - Women's)12/-11ReviewNoNoYesParka70014198,700N/AN/A3.6 oz 50D polyesterAround TownRegular880 g / 1 lb 15 oz79 cm / 31 in Arc'teryx Sensa (Women's)14/-10NoNoYesParkaN/AN/AN/ACoreloft Compact120 g/m²NP100d Gore-Tex 2LAround TownRelaxed785 g / 1 lb 11.7 oz86 cm / 34 in Patagonia Hi Loft Down (Men's - Women's)14/-10ReviewNoYesNoDown600177106,200N/AN/A1.4 oz 30D polyesterAll RoundRegular540 g / 1 lb 3 oz76 cm / 30 in REI Magma 850 Hoodie 2.0 (Men's - Women's)14/-10NoYesNoDown850120102,000N/AN/APertex mini ripstop nylonAll RoundRegular340 g / 13.75 oz74 cm / 29.25 in Arc'teryx Beta Insulated Coat (Women's)16/-9ReviewNoNoYesSyntheticN/AN/AN/ACoreloft 80 g/m² + 120 g/m²2L 40D Gore-TexAround TownRegular600 g / 1 lb 5.2 oz? Arc'teryx Atom AR (Men's - Women's)18/-8ReviewYes, meshNoNoSyntheticN/AN/AN/ACoreloft Continuous120 g/m2 + 80 g/m2 + 60 g/m230D TyonoAll RoundRegular475 g / 1 lb 74 cm / 29.1 in Patagonia Downdrift (Men's - Women's)18/-8NoNoNoDown600279167,400N/AN/A4.2 oz polyesterAround TownRegular1.014 kg / 2 lb 3.8 oz? Arc'teryx Magnus (Men's)19/-7NoNoNoParkaN/AN/AN/ACoreloft80 gN60p Gore-Tex 2LAround TownRegular690 g / 1 lb 8.3 oz83 cm / 32.5 in Arc'teryx Agrium (Men's - Women's)21/-6NoYesNoDown85011799,450N/AN/AAratoAll RoundRegular365 g / 12.9 oz75 cm / 29.5 in Patagonia AlpLight Down (Men's - Women's)21/-6NoYesNoDown80010080,000N/AN/A0.8 oz 10D polyesterAll RoundSlim270 g / 9.5 oz74 cm / 29 in Arc'teryx Beta Insulated (Men's - Women's)21/-6ReviewYes, zipsNoYesSyntheticN/AN/AN/ACoreloft Continuous80 g/m²2L 40D Gore-TexAll RoundRegular680 g / 1 lb 8 oz78.5 cm / 31 in Patagonia Topley (Men's)23/-5NoNoYesDown700172120,400N/AN/A6 oz polyesterAll RoundRegular1.133 kg / 2 lb 8 oz77 cm / 30.5 in Arc'teryx Alpha IS (Men's)23/-5NoYesYesSyntheticN/AN/AN/ACoreloft Continuous65 g/m²N40p-X 2L Gore-TexClimbingRegular610 g / 1 lb 5.5 oz78 cm / 30.75 in Rab Xenon 2.0 (Men's - Women's)23/-5NoYesYesSyntheticN/AN/AN/APrimaLoft Silver60 g30D Pertex QuantumAll RoundRegular385 g / 13.6 oz71.5 cm / 28.1 in Patagonia Down Sweater (Men's - Women's)23/-5ReviewNoYesNoDown800150120,000N/AN/A1.4 oz 20x30D polyesterAll RoundRegular428 g / 15.1 oz67 cm / 26.25 in Arc'teryx Ralle Parka (Men's)25/-4NoNoYesParkaN/AN/AN/ACoreloft 80 g/m²2L 40D Gore-TexAround TownRegular735 g / 1 lb 9.9 oz? Patagonia Silent Down (Men's - Women's)26/-3ReviewNoNoNoDown70010976,300N/AN/A2.2 oz polyesterAround TownRegular585 g / 1 lb 4.7 oz74 cm / 29 in Arc'teryx Therme Insulated (Men's)26/-3ReviewNoNoNoSyntheticN/AN/AN/ACoreloft Compact40 g/m²2L Gore-TexAround TownRegular960 g / 2 lb 1.9 oz73 cm / 28.75 in Arc'teryx Cerium (Men's - Women's)26/-3NoYesNoDown85011396,050Coreloft 80 + 100 g/m²Arato 15All RoundTrim335 g / 11.8 oz? Mountain Hardwear GW/2 (Men's - Women's)28/-2NoYesNoDown8008568,000N/AN/A10D Ripstop NylonAll RoundTrim250 g / 8.8 oz70 cm / 27.5 in Arc'teryx Cerium LT (Men's - Women's)28/-2ReviewNoYesNoDown85010286,700Coreloft 80 + 100 g/m²Arato 10All RoundTrim305 g / 10.8 oz72 cm / 28.3 in Arc'teryx Nuclei FL (Men's - Women's)32/0ReviewNoYesNoSyntheticN/AN/AN/ACoreloft Continuous65 g/m²Arato 10rClimbingTrim325 g / 11.5 oz75 cm / 29.5 in Patagonia DAS Light (Men's - Women's)34/1NoYesYesSyntheticN/AN/AN/APlumaFill65 g0.8-oz 10-denier Pertex Quantum ProClimbingRegular320 g / 11.3 oz77 cm / 30.5 in Patagonia Micro Puff (Men's - Women's)36/2ReviewNoYesNoSyntheticN/AN/AN/APlumaFill65 gPertex QuantumAll RoundTrim298 g / 10.5 oz75 cm / 29.5 in Patagonia Isthmus (Men's)36/2NoNoNoParkaN/AN/AN/AThermoGreen60 g4.2 oz polyesterAround TownRegular895 g / 1 lb 15.6 oz70 cm / 27.5 in Arc'teryx Proton (aka LT) (Men's - Women's)37/3ReviewNoNoNoSyntheticN/AN/AN/ACoreloft Compact80 g/m2 + 60 g/m2Fortius Air 20ClimbingTrim375 g / 13.2 oz75 cm / 29.4 in Patagonia Nano Puff (Men's - Women's)37/3ReviewNoYesNoSyntheticN/AN/AN/APrimaLoft Gold Insulation Eco60 g22D PolyesterAll RoundRegular363 g / 12.8 oz71.5 cm / 28 in Arc'teryx Norvan SL Ins. (Men's - Women's)39/4NoYesNoSyntheticN/AN/AN/ACoreloft Compact40 g/m²Gore-Tex ShakeDryRunningTrim270 g / 9.5 oz71.5 cm / 28.1 in Patagonia Nano Air (Men's - Women's)41/5ReviewNoNoNoSyntheticN/AN/AN/AFullRange60 g33D Nylon ripstopAll RoundTrim318 g / 11.2 oz? Arc'teryx Atom (aka LT) (Men's - Women's)43/6ReviewYes, meshNoNoSyntheticN/AN/AN/ACoreloft Continuous60 g/m²20D TyonoAll RoundTrim375 g / 13.2 oz74 cm / 29.1 in Arc'teryx Cerium SL (Men's - Women's)43/6ReviewNoYesNoDown8505849,300Coreloft 40 + 100 g/m²Arato 7All RoundTrim215 g / 7.6 oz69 cm / 27.2 in Arc'teryx Proton Hybrid (Men's - Women's)46/8ReviewNoNoNoSyntheticN/AN/AN/ACoreloft Compact40 g/m²Fortius™ Air 50All RoundTrim365 g / 12.9 oz? Arc'teryx Proton FL (Men's)48/9ReviewNoNoNoSyntheticN/AN/AN/AOcta Loft94 g/m²Fortius Air 20ClimbingTrim323 g / 11.4 oz77 cm / 30.4 in Arc'teryx Atom SL (Men's - Women's)52/11ReviewYes, meshNoNoSyntheticN/AN/AN/ACoreloft Compact40 g/m²20D TyonoAll RoundTrim245 g / 8.6 oz72 cm / 28.3 in REI Stormhenge Hybrid (Men's - Women's)TestingYes, zipsNoNoDown850?N/AN/A40D + 80DAll RoundRegular900 g / 1 lb 15.75 oz80 cm / 31.5 in Arc'teryx Monitor Insulated (Women's)TestingNoNoYesParkaN/AN/AN/ACoreloft80 + 100 g/m²40D 3L Gore-TexAround TownOversized645 g / 1 lb 6.8 oz93 cm / 37 in Arc'teryx Coelle (Women's)TestingNoNoYesParkaN/AN/AN/ACoreloft80 + 140 g/m²40D 2L Gore-TexAround TownRegular460 g / 1 lb 0.2 oz93 cm / 37 in

View full table at https://outdoorcrunch.com/best-arcteryx-jacket/. 

If you're confused now and don't know which jacket best corresponds to your own needs, then follow the advice given in https://arcteryx.com/us/en/shop/jacket-finder/. 

The temperature ratings in this list are intended to represent the lowest temperatures you can wear each jacket without feeling uncomfortably cold. 

Keep in mind that these are only approximate values, assuming: 

These values applicable to your torso only. Your hands, legs and feet are still subject to their own additional insulation.

The best practice is usually to use this table for comparing each jacket to one another, rather than pinpointing their ratings. 

Also, ratings will best respond to males. As most women tend to run colder than men, for women, shifting these ratings a bit is recommended. 

Always opt for the warmer option when in doubt. For jackets with Atom AR level warmth and beyond, recommended is almost always the hooded models. 

I'm not going to explain the Coreloft insulation in detail because both jackets are equipped with it. I'll try to keep this post within the context of differences between these products.

First of all, the AR does NOT have twice the insulator amount of LT.

AR is insulated with: 

LT, on the other hand, is insulated with 60 g/m2 of Coreloft everywhere. 

This makes up one of the biggest differences between the two models: AR is significantly warmer compared to LT. If you're truly active inside the AR, you might even overheat. 

Poll results: Best colorways of Atom Series

Upvote your favorites.

Black

Kingfisher

Void

Canvas

Quick links:

https://arcteryx.com/shop/mens/atom-lt-jacket

https://outdoorcrunch.com/arcteryx-proton-lt-vs-atom-lt/

Void

Canvas

Black

Solace

Heritage

Fika/Black Sapphire

Kingfisher

Quick links:

https://arcteryx.com/shop/mens/atom-lt-hoody

https://outdoorcrunch.com/nano-puff-vs-atom-lt/

Serene

Black

Canvas

Jungle Maze

Sprint

Solitude

Quick links:

https://arcteryx.com/shop/mens/atom-sl-hoody

https://outdoorcrunch.com/arcteryx-atom-lt-vs-sl/

Techno

Atmos

Sprint

Black

Orca

Solace

Fika/Spark

Black Sapphire

Expanse

Velvet Sand

Labyrinth

Quick links:

https://arcteryx.com/shop/womens/atom-hoody

Wicker/Sprint

Solitude

Groovie

Black

Bliss/Spark

Serene

Quick links:

https://arcteryx.com/shop/womens/atom-lightweight-hoody

Black

Solace

Quick links:

https://arcteryx.com/shop/womens/atom-jacket

Synth

Habitat

Moonlit

Black

Quick links:

https://arcteryx.com/shop/womens/atom-heavyweight-hoody

Now, although it's quite difficult to pinpoint the warmth differences between these two jackets, let me do my best and at least try to give you an idea:

Generally speaking, with only a long sleeved shirt under and without a shell on top, for an average person, during daily use (strolls, power walks, etc) and with enough wind to cause an umbrella to twist in your hand:

...without feeling uncomfortably cold, the lowest temperature to wear an Atom LT would be 36 deg F (2 deg C), and Atom AR around 18 deg F (-8 deg C).

With at least a moderate quality layering:

...Atom LT would be at 25 deg F (-4 deg C), and AR at 7 deg F (-14 deg C).

With a good base layer under and a shell jacket on top:

...Atom LT would be at 10 deg F (-10 deg C), and AR at -4 deg F (-20 deg C).

Links: 

Note that AR can even come too warm when you near 40 F's. 

Maybe this entire thing can be oversimplified into this:

If you're looking for a warm jacket to put on out in the town when it's freezing with shitty wind, do not get an LT! You'll probably feel too cold inside it!

Although it breathes poorly, AR is much warmer and wind resistant - which makes it excellent for stationary use.

Although side fleece panels of LT make it much more breathable, it sacrifices wind resistance significantly.

Although both these jackets are marketed as mid layers (meaning you need an extra layer over them), with the AR, you won't need a shell unless there's heavy rain.

With the LT, though, you probably will.

Speaking of rain, both jackets come with DWR coating at the top - although they're mid layers.

What is DWR by the way?

DWR is a coating. 

It's basically sprayed on to the surface of these jackets as a finish. It stands for Durable Water Repellent - which means that water will be repelled under wet conditions instead of soaking into the fabric. 

DWR also decreases dry time. 

It's a good thing these jackets are coated in DWR, but pay attention to the fact that DWR is a coating - meaning that it will wear off over time. 

Which is why you might want to invest in a DWR spray such as this one for after treatment. 

As you see, there's a strong correlation between FP x FW and temperature ratings, but not more than, say, 80%. I explained why this happens here in this post of mine. 

So the winner is AR by far.

Side panels help LT breathe perfectly during skiing as well as any other activity that requires high mobility.

Until this point, I've repeated it many times, but for the sake of consistency let me say it one more time:

LT is much more breathable than AR due to its side fleece panels.

This is also what causes AR to overheat much easier compared to LT.

If you're active, OR it's nearing 30 F's out, AR probably will start feeling too warm, even if it isn't layered with anything else.

That said, LT still isn't the BEST in terms of breathability.

I don't want to confuse you even further, but note that in our post Patagonia Nano Air vs Arcteryx Atom LT, we found that the Air is actually more breathable - although less weather resistant and more, ugh, "frumpy" looking.

First of all, LT comes with a trim fit and AR with a regular fit. If you have an athletic build, LT would probably look very good on you. AR, on the other hand, is more "bulky".

If you'd like to see some numbers:

Atom LT Hoody (Medium)

Atom AR Hoody (Medium)

Note: The small sizes are roughly 5 cm smaller in the chest and waist.

This is how Trim and Regular Fits are illustrated by Arcteryx:

Men's fit. LT comes with a trim fit and AR with a regular fit. 

Women's fit. LT comes with a trim fit and AR with a regular fit. 

Another thing about fit is that AR is thicker and more puffy going outwards: 

That said, the "puffiness" difference isn't big enough to cause a difference when you're trying to layer a shell on top.

At 0.9 lbs (415 grams), LT is only 0.1 lbs lighter compared to AR's 1 lb (470 grams) of weight.

If you'll be wearing the jacket out in the town only, this won't be a noticeable difference.

However, for activities that require physical strength and endurance, this difference will make a difference for most of us.

You can use LT pretty much doing any outdoor activity, such as:

You name it.

kelly Starr (@kstarr45)'in paylaştığı bir gönderi (4 Şub, 2017, 11:53öö PST)

*Biking & rocking LT's.

On the other hand, AR would be too warm and uncomfortable for all of these activities. It'd be more suitable for casual, frigid weather outgoings, though.

They're even marketed that way by Arcteryx themselves.

So I don't thing we can say one is more versatile than the other, since one can't replace the other's work. Just choose according to your own needs and desires.

So... in short: 

If you're going to be physically active, absolutely get the Atom LT since it's more breathable. For a stationary use, absolutely get the Atom AR since it's warmer and more weather resistant.

Trekitt's reviews on these jackets also worth checking out:

Atom AR:

Atom LT: