"A Jacket That 'Slims Down' When You Sweat": Bacterial Cellulose Taught Clothes to Self-Regulate Heat

Science Advances described a “smart” warm fabric, whose filling is made of natural bacterial cellulose, which reacts to sweating: when it is humid around the body, the material automatically becomes thinner, and when it is dry, it again gains “puffiness” and retains heat. In the prototype, the thickness changed from about 13 mm (dry) to 2 mm (humid), and the general idea is to extend the time of thermal comfort without electronics and batteries.

Background

What have you tried before:

1. Phase change materials (PCMs) in microcapsules “swallow” heat during melting and release it during crystallization, but operate in a narrow temperature window and react poorly to real sweating.
2. Radiant fabrics based on nanoporous polyethylene (nanoPE) allow the body's thermal IR radiation to pass through, providing passive "radiative cooling", but this is essentially a channel for removal, and not "self-regulation of insulation" during sweating.
3. Humidity actuators/hygromorphic fabrics change shape/pores when humidity increases, expanding the “comfort zone” without wires - the direction is rapidly maturing.

• The problem that “smart” fabrics solve. Thermal comfort of clothing collapses when activity changes rapidly: overheating and sweating during effort, hypothermia due to a damp layer when stopping. Therefore, adaptive thermal/moisture textiles have been rapidly developing in recent years, which adjust heat exchange without batteries and complex electronics. Reviews emphasize the key vector - dynamic management of heat and moisture at the fiber/fabric layer level.
• Why humidity/sweat is the best "trigger". Sweat is the main quick marker of overheating: as soon as local humidity increases, the system needs to reduce thermal resistance (less "puffiness"/air chambers) and increase evaporation; when it dries out, return the insulation. Hence the idea of materials that automatically respond to humidity, not to external temperature. This saves energy and avoids bulky electronics.
• What is bacterial cellulose and why is it promising? BC is a biopolymer that is “grown” by acetic acid bacteria ( Komagataeibacter ): it forms a nanofibrillar network with high water capacity, strength, air permeability and biocompatibility. In textiles/materials science, BC is valued for its sensitivity to moisture and sustainable production from renewable raw materials.
• A scientific gap that a new article closes. Most passive solutions either remove heat (radiative) or buffer it (PCM), weakly considering that humidity itself should "switch" the insulation. The work in Science Advances uses the BC layer as the "heart" of warm clothing, which thins with sweat (less air → less insulation) and straightens out again when dry - that is, it builds self-regulating thermal insulation based on body humidity.
• Field context: where does this fit in? The trend is toward passive, bio- and polymer systems that expand the “comfort window” without the user’s energy. Next to them are: new generation hygromorphic actuators (showing a noticeable expansion of the comfort zone) and cellulose/bio-based radiative cooling — BC fits well into this “green” branch of personal thermal management.
• Practical implications for industry: If the moisture-controlled “plumpness” of BC insulation is confirmed in wearable testing (wash, wear, odors, response threshold tuning), manufacturers will have a scalable, bio-based filling for winter/active layers — with less overheating on the go and less shivering at rest. This is complementary, not competitive, to radiant and PCM solutions: they can be combined in multilayer systems.

How it works

• The bacterial cellulose (BC) filling is a natural "net" of nanofibrils produced by harmless bacteria (familiar to everyone from tea fungus/kombucha). This membrane is light, durable, breathable and hydrophilic - it "senses" moisture perfectly.
• When you start sweating, the local humidity under the clothes increases, the fibrous layer loses its "puffiness" and flattens out - less air inside → less insulation → it is easier for the body to lose excess heat. As soon as you dry out, the structure straightens out again and returns a high level of thermal insulation due to the air between the fibers. It is a simple passive mechanism that works on moisture, not electronics.

What the authors showed

• Adaptation to sweat and moisture. In dry conditions, the material maintains a maximum thickness of ~13 mm, and at high humidity (simulating sweating) it thins to ~2 mm. Due to such "variable thickness", the prototype significantly extends the time of thermal comfort compared to conventional warm fabric, especially when changing the "rest → load" mode.
• The principle is scalable. The authors emphasize that the “filling” can be sewn into different types of clothing — from linings to insulating layers — and adjusted to the climate/load.

Why is this necessary at all?

Classic warm clothing is a compromise: the warmer the layer, the higher the risk of "overheating and sweating", and then overcooling due to the wet undergarment "mini-sauna". Textiles, which weaken the insulation during sweating and return it when dry, help to maintain the "golden mean" without unnecessary zippers, valves and batteries. Moisture plays a key role in human thermal management (heat is carried away by evaporation), so "smart" fabrics are increasingly learning to react specifically to moisture/humidity.

How is this different from other smart fabrics?

• No electronics. Unlike active systems (thermoelements/soft robotics), here it is pure physics of the material: wet → thinner, dry → thicker. It is simpler, cheaper and potentially more durable.
• Not "valves", but "plumpness". Previously, fabrics with moisture valves/pores or with an accordion thickness on polymer inserts were offered. Now the role of the "accordion" is taken over by natural bakcellulose, already known in medical dressings and "green" textiles.
• Eco-potential. Bacterial cellulose is biocompatible and biodegradable, can be grown without cotton and oil, and its production is in line with the current trend towards sustainable materials.

Where this can be useful

• Winter in the city and "office-street-subway". Changes in activity and climate "throw" the body into heat/cold less - comfort "lasts" longer.
• Mountain/running activities. During the climb/run the fabric ventilates, and at a rest stop it insulates again.
• Field and production conditions. The fewer moving parts and electronics, the more reliable. (Plus plus for the light weight and "breathability" of the BC.)

Restrictions

This is still a scientific development and prototype; it still needs to be tested for everyday wear:

• Durability and washability (multiple cycles of wetting and drying, "dry cleaning of life"),
• Skin comfort and odors when worn for long periods of time,
• Setting up the response “thresholds” for different climate/sweating profiles,
• Cost and scaling of growing bakcellulose to rolls of fabric. For comparison: the field of "thermoregulating" fabrics is actively growing, but only a part of the ideas reach the mass market.

Conclusion

"Clothing that adapts to sweat" is a logical continuation of a decade-long search for moisture-sensitive and temperature-sensitive textiles. A new paper in Science Advances adds natural bacterial cellulose to the field as the "heart" of adaptive insulation and shows a large amplitude of thickness change (13 → 2 mm) along with an increase in thermal comfort time - without wires and sensors.

Source: Sweat-sensitive adaptive warm clothing, Science Advances (AAAS), 2025. DOI: 10.1126/sciadv.adu3472