Most hunters look at insulation numbers and marketing claims and assume they know which jacket is warmer. But from testing a massive group of cold-weather jackets over the last two years, I know it’s never that simple. Fit, construction, fabric, windproofing, insulation type, and thermal inertia all matter.

Last season, I tested seven of the top cold-weather whitetail jackets on the market — Sitka Fanatic, ASIO Late Season, Kryptek Vellus, Pnuma Highpoint, Huntworth Matterhorn, and more. That series exploded here on the site and YouTube.

But a ton of you kept asking the same thing.

“Can you test the First Lite Core and the First Lite Thermic?”

At the end of last season I couldn’t. First Lite released them too late to test properly. But this year I finally ran both jackets through my full heat-retention test, wore them in the field, and analyzed their insulation and construction in depth.

The results were surprising.

Why You Should Trust This Review

My name is Mike Manley, founder of The Everyday Bow Hunter and retired U.S. Army Special Forces Sergeant Major. I’ve spent decades testing gear; first for the military and now for bowhunters.

I test cold-weather jackets using:

• Thermal mannequins wearing identical base layers
• Chest-mounted heating pads benchmarked to the same output
• Temperature probes under the armpits for consistent data
• Identical test duration (60-minute heat-up + 2-hour cool-down)
• A fixed ambient temperature of 64°F
• Repeated testing to average out anomalies

This takes personal preference and “I felt warm” out of the equation.

The data speaks for itself.

First Lite Thermic vs Core: What’s the Difference?

On paper, these jackets look similar, but insulation weight and outer fabric separate them into two completely different categories.

First Lite Core Jacket: Overview – See it here

• 80gsm PrimaLoft Gold Insulation (body)
• 60gsm PrimaLoft Gold Insulation (arms)
• 100% windproof
• Very quiet, very soft
• Extremely comfortable
• Not very durable in brush
• 2 lbs 6 oz (jacket only)

This is a mid-to-late season whitetail jacket designed for quiet sits in moderate cold. Think 25 to 50 degrees depending on your layering. Very packable for a mid-late season jacket.

The comfort is elite. It feels like wearing a soft fleece hoodie. But thin brush can and will chew it up.

First Lite Thermic Jacket: Overview – See it here

• 170gsm PrimaLoft Gold Insulation (body)
• 133gsm PrimaLoft Gold Insulation (arms)
• Sherpa-fleece lining
• Windproof soft shell exterior
• Much more durable in brush
• 4 lbs 2 oz (jacket only)

This is a true late-season jacket, built for 20 degrees and below. If you’re hunting the coldest days of the year, this is the insulation class you want.

It’s heavier, bulkier, and not nearly as packable, but the warmth and brush resistance are in a different league compared to the Core.

Shared Features (Both Jackets)

Both jackets share First Lite’s whitetail platform:

• Removable hood
• Articulated collar for bowhunting
• Exterior chest pockets designed to stay accessible under a bino harness
• KitLink hand-warming system
• 100% windproof membrane
• DWR water resistance
• Safety harness port
• Silent fabrics
• Quiet snaps (except on the wrists where they are normal, noisy snaps)

Both are purpose-built bowhunting jackets and both are extremely quiet.

Durability Differences

This is one area where the jackets are not equal.

Core Jacket Durability

The Core is incredibly soft and quiet but does not like brush.

Light briars will fuzz it. Jaggers will grab and pull threads. Burrs stick everywhere.

It’s perfect for:

• Walking clean trails
• Climbing into preset stands
• Minimal brush exposure
• Carrying in and putting on at the tree

But it is not a bushwhacking jacket.

Thermic Durability

The Thermic uses a soft-shell exterior similar to First Lite’s Whitetail Catalystand Phase. It’s:

• Quiet
• Much tougher
• More resistant to jaggers
• Far less prone to burrs

If you’re pushing through thick mountain laurel or briars, the Thermic can handle abuse better.

Heat Retention Testing: The Real Numbers

This is where the data becomes clear.

How the Test Works

• Both jackets start at ~64.5°F
• Heating pads warm them for 60 minutes
• I record how much heat they capture
• I shut the heat off
• I track the temperature for 2 hours of cooling

This allows me to see:

• Heat-up speed
• Heat absorption
• Thermal inertia
• Long-term retention

Here are the numbers:

Thermic Heat-Up

• Heat gained: +19.6°
• Peak temperature: 85.1°F
• 2-hour final: 71.9°F
• Total heat retained: 6.4° (32.6% retention ratio)

Core Heat-Up

• Heat gained: +14.6°
• Peak temperature: 80.8–80.9°F
• 2-hour final: 71.0°F
• Total heat retained: 4.7° (32.1% retention ratio)

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The takeaway:

• Thermic is clearly the warmer jacket. It reaches a much higher peak, heats faster, and provides more warmth during the first hour of a cold sit — where the real comfort difference is felt.
• Core cools slower. It bleeds heat at a slower rate because it has less insulation mass. That’s normal.
• Both end up nearly identical after 2 hours. 71.9°F vs 71.0°F is essentially the same long-term equilibrium.

This matches what we see with other jackets:

• High-insulation jackets heat high and drop quickly
• Low-insulation jackets heat lower but drop slowly
• They converge over long sits

Field Test Results

I wore both jackets in 25–40 degree temps with my normal thermal layering setup:

• Brynje mesh base layer
• First Lite Wick hoodie
• Rugged Wool Quarter Zip
• Corresponding bibs

Core in the field:

• Warm at 29 degrees
• Never got cold
• Very quiet
• Hood performed well
• Pockets stayed warm even before hand warmers
• Extremely comfortable
• Perfect for “clean” access routes
• Not good for heavy brush

Thermic in the field:

• Outstanding warmth
• Built for 20 degrees and below
• Much more durable
• Soft-shell exterior sheds briars and burrs
• Heavy, but that’s normal for true late-season insulation
• Performs in the same class as ASIO Late Season and Pnuma Highpoint

How the Thermic and Core Compare to Other Jackets

Based on last year’s test of seven top jackets:

Peak Warmth Ranking (out of 9 jackets tested)

1. Huntworth Matterhorn
2. Pnuma Highpoint
3. First Lite Thermic
4. ASIO Late Season
5. True Timber Down Parka
6. Kryptek Vellus
7. Sitka Fanatic
8. First Lite Core
9. Pnuma Vintis

Long-Term Retention (2-hour performance)

1. Pnuma Highpoint
2. ASIO Late Season
3. First Lite Thermic
4. Huntworth Matterhorn
5. Sitka Fanatic
6. First Lite Core
7. Kryptek Vellus
8. True Timber Down
9. Pnuma Vintis

Which Jacket Should You Buy?

Buy the First Lite Core if: (Get it here)

• You hunt 30–50 degree sits
• You want a quiet, comfortable jacket
• You won’t be busting brush
• You want high warmth-to-weight efficiency
• You want something very packable

Buy the First Lite Thermic if: (Get it here)

• You hunt 20 degrees and below
• You want maximum warmth
• You need durability in brush
• You want a top-tier late-season jacket
• You don’t care about weight (warm coats are heavy — period)

Final Verdict

The First Lite Thermic is the warmer, more capable cold-weather jacket.

It heats higher, warms faster, and offers true late-season performance.

The First Lite Core punches above its weight.

It’s one of the best mid-to-late-season jackets I’ve tested and an outstanding bowhunting layer for 25–50 degrees. Just don’t take it through heavy brush.

Both jackets deliver exactly what their insulation tells you, but the Core’s efficiency is impressive, and the Thermic is absolutely in the top tier with the warmest jackets I’ve ever tested.