Close to the body, not tight.

The heat works best when the panels sit against you. So it's cut close, but with enough stretch to stay comfortable all day. These are body measurements. Measure yourself, not a shirt. Allow ±0.5–0.75" (1–2 cm).

1. Measure your chest. Stand relaxed. Wrap a soft tape under your arms, around the fullest part of your chest. Keep it level across your shoulder blades. Snug, not tight.
2. Measure your sleeve. Bend your arm slightly. Measure from the centre back of your neck, over your shoulder, down the outside of your arm to your wrist.
3. Pick your size. Wearing it under a jacket or gilet? Stay true to size. Wearing it over other clothes? Size up. We've updated our size labels based on customer feedback. If you've ordered before, check the chart again. Your size may have changed.

Between sizes, broad shoulders or an athletic build? Size up. Because the fit is close, the next size won't feel baggy. Still not sure? Email us your measurements and we'll tell you which size to get. And if it doesn't fit, our 60-Day Fit Guarantee covers free size exchanges.

Warm your body, not the whole room.

Cold mornings. Long commutes. Hours on the sidelines. Thick layers keep some of the cold out, but they make you bulky and stiff. HearthLayer puts the heat right against your core, elbows and back, under whatever you already wear.

• Warm in 30 seconds. 16 ThermoSphere™ heat panels cover your core, elbows and back. Hold the button, and you feel the heat within 30 seconds.
• Heat you control. Three levels: Low, Medium and High. One press switches between them. Go from a gentle boost indoors to serious warmth outside.
• All day on one charge. Up to 12 hours on Low with the included 10,000 mAh power bank.
• No bulk. The panels are ultra-thin, flexible carbon, built into stretch fabric. No stiff wires. It slips under a coat without the Michelin-man look.

Where it works best: commuting, outdoor work, walking, spectating, camping, motorcycling, skiing, and staying warm at home. It's made for low-to-moderate activity. During hard runs or intense training, most people heat up fast and won't need it.

Try it for 60 days. If it's not for you, our 60-Day Money-Back Guarantee has you covered.

Built to stay safe. It runs on 5V USB — the same voltage as charging your phone. Built-in sensors keep the heat steady and adjust it automatically if it gets too hot. FCC certified.

What is it made of?

• Soft stretch polyester — a regular-fit base layer that moves with you
• 16 ThermoSphere™ carbon panels — ultra-thin and flexible, across your core, elbows and back
• Sealed, insulated heating elements — so the electronics survive the washing machine
• Internal power bank pocket — low-profile, near the hem, with a short routed cable

How do I wash it?

• Take the power bank out first. Unplug it and remove it from the pocket every time.
• Machine wash cold. Zip it up, put it in a laundry bag, and use a gentle cycle.
• Line dry only. No tumble dryer.
• Skip the harsh stuff. No bleach, no ironing, no dry cleaning. They can damage the heating panels.

What's in the box

• 1 HearthLayer™ Heated Baselayer with 16 ThermoSphere™ panels
• 1 10,000 mAh power bank (up to 12 hours of heat)
• 1 USB cable for charging your power bank

Wear it every day. It's machine washable, so you can treat it like any other base layer. Just remember: power bank out before it goes in the wash.

The power bank is included.

Every order comes with our 10,000 mAh power bank. That gives you up to 12 hours of heat on Low. Medium and High use more power, so the heat lasts a shorter time.

How to turn it on

1. Plug in the power bank. Connect it to the cable and tuck it into the internal pocket near the hem.
2. Hold the button for 3 seconds. The light comes on and you feel the warmth within 30 seconds.
3. Press to change the level. Each press cycles through Low, Medium and High. The light colour shows your setting.

Power

• 5V USB. Low voltage, no mains electricity, no exposed wiring.
• Works with any standard 5V USB power bank. Handy if you want a spare for longer days.
• Automatic temperature control. Sensors watch the heat and adjust it so it never goes past your chosen level.

Charge it overnight. Plug the power bank in when you take the base layer off. It's ready for the whole day by morning.