By the Hikesity Editorial Team
"Infrared" and "far-infrared" show up on almost every thermal top these days, usually next to a bold number like "+5°C." So what does it actually mean — and can a tank top really make you five degrees warmer without turning you into the Michelin Man? Here's the honest, plain-English version, plus how our CatWarm Infrared Thermal Tank uses Japanese Hush Fiber to stay thin and warm at the same time.
What is Japanese Hush Fiber?
Japanese Hush Fiber is an ultra-fine, high-loft knit engineered specifically to manage body heat. Instead of relying on thickness (the old way — more fabric, more bulk), it uses a densely structured far-infrared yarn that traps a layer of warm air close to the skin and reflects your radiated body heat back toward you. The result is a fabric that feels barely-there on but performs like a much heavier layer.
How does far-infrared thermal fabric keep you warm?
Your body constantly radiates heat as far-infrared energy. A normal cotton or thin synthetic tank lets most of that heat pass straight through and escape. A far-infrared fabric like Hush Fiber does two things at once:
- Reflects your own far-infrared body heat back toward your skin instead of letting it radiate away.
- Traps a thin, stable layer of warm air in its knit structure, reducing convective heat loss.
Because it works with the heat you already produce, there's no battery, no chemical warmer, and no waiting — it starts conserving warmth the moment you put it on.
What does "+5°C" actually mean?
Here's the honest framing most brands skip. "+5°C" is a comparative warmth figure: in testing, the far-infrared knit measured up to about 5°C warmer against the skin than a plain base layer of the same thickness, under the same conditions. It does not mean the shirt heats itself to a fixed temperature or raises your core body temperature by five degrees. The value comes from how efficiently the fabric conserves your heat — which is exactly why a thin Hush Fiber layer can outperform a much thicker ordinary one.
Hush Fiber vs a regular thermal base layer
| Japanese Hush Fiber | Standard thick thermal | |
|---|---|---|
| Warmth mechanism | Far-infrared reflection + trapped warm air | Bulk / thickness only |
| Thickness | Ultra-thin, layers invisibly | Bulky under clothes |
| Breathability | Breathable, low sweat build-up | Can trap moisture |
| Wear solo? | Yes — finished look | Usually underwear-only |
Thin matters: warmth without the bulk
The whole point of an infrared knit is that you don't have to choose between warm and sleek. A Hush Fiber tank slips under a sweater, blouse, or jacket without adding a visible layer or bunching at the waist — so it works as a winter base layer and as a top you can wear on its own.
The bonus: a built-in removable bra
Warmth is only half of what makes a thermal tank worth wearing every day. The CatWarm Infrared Thermal Tank adds a built-in removable bra — molded pads that give real shaping and coverage, not just a loose "shelf bra" elastic band. Take the pads out to wash them, or leave them in for a clean, seamless line under clothes. One piece replaces a tank plus a bra.
How to wear it all season
Wear it solo as a U-neck top in transitional weather, or layer it invisibly under sweaters and coats when it gets cold. For very cold or active days, pair it with the matching CatWarm Thermal Leggings for head-to-toe infrared warmth. For a full breakdown of styles and fits, see our guide to the best thermal base layers with a built-in bra.
FAQ
Does infrared thermal fabric really keep you warmer?
Yes. Far-infrared fabric reflects the body heat you already radiate back toward your skin and traps a thin layer of warm air, so a lightweight knit retains noticeably more warmth than a plain layer of the same thickness. It conserves your heat rather than generating heat.
How much warmer is a Hush Fiber infrared tank?
In testing, the far-infrared Hush Fiber knit measured up to about 5°C warmer against the skin than a plain base layer of the same thickness under the same conditions. That's a comparison of warmth retention — not a claim that the fabric heats itself to a set temperature.
Is an infrared tank a good winter base layer?
It's ideal. Because Hush Fiber is ultra-thin, it adds warmth without bulk under your outer layers and stays smooth instead of bunching — so it layers invisibly while doing the work of a much heavier thermal.
What is a removable bra pad, and how is it different from a shelf bra?
A shelf bra is just an inner elastic band with minimal support. A removable bra uses molded pads that give real shaping and coverage, and you can take them out to wash them or wear the tank without them.
How do I care for it?
Machine wash cold on a gentle cycle and lay flat or hang to dry to protect the stretch and the infrared finish. Remove the bra pads before washing if you prefer.
