The 221B Tactical Equinoxx K2 Dyna-Thermal is a triple-layer thermal base layer shirt built for serious cold-weather performance, rated for temperatures below 15°F (-9.45°C). Designed as a full-coverage complement to the popular Equinoxx Stage 3 Thermal, the K2 extends 360-degree thermal protection from just below the waist to just below the chin, making it a complete single-layer cold-weather solution for outdoor workers, law enforcement, and recreational users. It retains body heat, blocks wind, and resists rain — all without the bulk of a heavy jacket. Available in standard shirt sizing.

Who this is for

• Outdoor professionals: postal workers, construction crews, linemen, oil rig workers, and anyone else logging long hours in cold, wet, or windy conditions who needs full mobility on the job.
• Law enforcement and security personnel: officers who need a standalone cold-weather base layer for off-duty or recreational use, or who want 360-degree torso coverage that the Stage 3 (designed around body armor) does not provide.
• Cold-weather recreational users: hunters, hikers, skiers, motorcyclists, and anglers who want a single packable layer that performs in sub-freezing temperatures without restricting movement.

Thermal performance

The K2 carries a temperature rating of sub-15°F (-9.45°C), achieved through a heat-pressed, triple-layer fabric construction. The outer layer is a stretchy polyurethane fabric. The middle layer resists water and blocks wind. The inner layer is a soft grid-thermal fleece that sits directly against the skin.

The grid design of the inner fleece liner reduces fabric weight while increasing warmth and compressibility. The grid channel structure creates targeted touch points that absorb and diffuse moisture vapor for faster evaporation, improving both wicking efficiency and breathability. The result is a base layer that keeps you warm during low-activity cold exposure and vents adequately when your output increases.

Construction and fit

The K2 is soft, stretchy, and non-bulky. The mock neck design extends coverage just below the chin. Extended compression sleeve cuffs keep the sleeves seated under gloves or outerwear. An extended torso length keeps the shirt tucked during dynamic movement. The regular fit is form-close without being compressive, and the polyurethane outer layer gives the fabric a degree of stiffness that is functional rather than uncomfortable — it contributes to wind blocking and shape retention during wear.

For sizing, choose your standard shirt size. If you fall between sizes, size up for a more comfortable fit over other layers.

Specifications

Frequently asked questions

How does the K2 differ from the Equinoxx Stage 3 Thermal?

The Stage 3 is designed specifically as a body armor base layer, and its coverage accounts for the fact that body armor covers the mid-section. The K2 provides the same features but adds full 360-degree thermal protection from just below the waist to just below the chin — making it the better choice when you are not wearing a plate carrier or soft armor vest.

Can I wear this under body armor?

Yes. Officers and security personnel who already use the Stage 3 under their armor may find the K2 more useful as an off-duty cold-weather layer, since the full torso coverage it provides would be largely redundant under a vest. That said, the K2 will fit under most body armor carriers without adding significant bulk.

Will one layer be enough in extreme cold?

The K2 is rated for sub-15°F conditions as a standalone base layer. User experience in conditions ranging from -15°C to -20°C with only a light outer shell or hoodie on top confirms effective heat retention at those temperatures. In truly extreme wind and cold, pairing it with a shell jacket extends performance further while still eliminating the need for multiple inner layers.

How should I size this?

Choose your standard shirt size. Because the K2 is designed to be form-fitting, size up if you are between sizes — especially if you plan to wear a light layer on top. The extended cuffs and torso length are built into all sizes.

Can I machine wash this?

Yes. Machine wash cold. Hang dry is preferred; tumble dry on low is acceptable. Avoid high heat, which can degrade the polyurethane outer layer and the heat-pressed construction over time.

Is this only for law enforcement, or is it suitable for general outdoor use?

It works for anyone who spends time outdoors in cold weather. The product is well-suited for construction workers, delivery and postal workers, crossing guards, hunters, motorcyclists, skiers, and hikers. The 221B Tactical lineage in law enforcement gear means the construction skews toward durability and functional performance rather than casual streetwear aesthetics.