Innovation·Powers the better World
I. Introduction
Y-Warm is a nanoscale, closed-cell, flexible thermal insulation material developed by Y-Warm Technologies Co., Ltd. over eight years of research and development. Its core technological breakthrough lies in overcoming one of the major mechanical limitations of conventional aerogels—their inherent brittleness—while maintaining an ultra-low thermal conductivity comparable to that of aerogels, at approximately 0.020 W/(m·K).
One of Y-Warm’s most distinctive features is its ability to combine moisture permeability and quick-drying performance with highly efficient thermal insulation—properties that often involve trade-offs in conventional insulation materials.
This paper examines the intrinsic mechanisms through which Y-Warm’s closed-cell structure enables moisture permeability and rapid drying, beginning with an analysis of the material’s microstructure.
II. Microstructural Characteristics of Y-Warm’s Closed-Cell Structure
Based on three-dimensional reconstructions obtained through nano-CT imaging and characterization by scanning electron microscopy (SEM), Y-Warm exhibits a typical honeycomb-like internal morphology consisting of nanoscale cell walls and discrete, isolated pores on the micrometer scale.
Its key structural parameters are as follows: The defining characteristic of a closed-cell structure is that individual pores are isolated from one another, with no continuous gas channels connecting them.
Cell wall thickness: 20–280 nanometers
Pore size: 30–190 micrometers
Closed-cell rate: ≥95%
Effective porosity: ≥96% (excluding the substrate)
Surface density: approximately 46 g/m²
Finished product thickness: 0.7 mm (YW-01 model)
From the perspective of porous-material theory, closed-cell structures can provide superior thermal insulation compared with open-cell structures because the isolated cells suppress gas convection pathways. Meanwhile, the stationary gas enclosed within each cell—N₂ serving as the carrier gas in Y-Warm—further limits heat transfer through the gaseous phase.
In general, thinner cell walls and lower material density can reduce solid-phase heat conduction and increase overall thermal resistance, thereby contributing to greater thermal insulation efficiency.
III. Structural Mechanisms of Moisture Permeability
3.1 Chemical Introduction of Hydrophilic Groups
Y-Warm does not rely solely on its physical structure to achieve moisture permeability. Hydrophilic functional groups are also incorporated into its polymer matrix at the molecular level.
These hydrophilic groups can form hydrogen bonds with water molecules, giving the material an inherent affinity for water vapor. When water vapor evaporating from the skin comes into contact with the inner surface of Y-Warm, the hydrophilic groups rapidly capture and adsorb water molecules onto the polymer chains.
Test data indicate that Y-Warm’s moisture absorption capacity is nearly twice that of the standard reference sample.
3.2 The “Adsorption–Transport–Release” Pathway Through Closed-Cell Walls
Although the individual pores are closed, the polymer matrix forming the cell walls constitutes a continuous solid phase.
Once water molecules are captured by hydrophilic groups, they can migrate through the polymer matrix at the molecular level, driven by the concentration and vapor-pressure gradients between the inner side (high-humidity side) and the outer side (low-humidity side).
This process can be described by Fickian diffusion. The diffusion rate of water molecules through the polymer matrix is influenced by factors including the hydrophilicity of the matrix, diffusion-path length, and the water-vapor pressure difference between the two sides of the material.
Because Y-Warm’s cell walls are only 20–280 nanometers thick, the diffusion distance that water molecules must travel through the solid-phase walls is extremely short. This short transport pathway can substantially reduce the time required for moisture to migrate through the material.
In other words, Y-Warm’s moisture permeability does not depend on continuous open pores that allow air to pass directly through the material. Instead, water vapor can be transported through the continuous polymer phase via a molecular-scale “adsorption–diffusion–release” mechanism.
This distinction is important because it helps explain how a material can maintain a predominantly closed-cell structure for thermal insulation while still allowing moisture vapor to migrate across it.
3.3 Rough Surface Morphology and Increased Specific Surface Area
The front surface of Y-Warm exhibits a rough microstructure associated with its micrometer-scale porous morphology. This surface roughness substantially increases the material’s effective specific surface area, exposing more hydrophilic functional groups and thereby increasing the area available for interaction with water vapor.
The increased surface area can therefore facilitate moisture adsorption and subsequent transport through the material.
At the same time, Y-Warm exhibits high infrared emissivity and corresponding far-infrared radiative properties. These characteristics may contribute to radiative heat exchange at the material surface and, under appropriate conditions, may assist the evaporation of surface moisture, thereby supporting the material’s quick-drying performance.
IV. Structural Mechanisms of Quick-Drying Performance
4.1 Physical Basis for Rapid Evaporation
Test data indicate that Y-Warm’s evaporation rate is approximately twice that of the standard reference sample, and that the material can dry completely in approximately one hour under room-temperature conditions after becoming wet. This rapid-drying performance is closely associated with its closed-cell structure and ultra-thin, highly porous morphology.
First, the closed-cell structure helps limit the accumulation of liquid water within the internal pores. Unlike open-cell foam materials, in which liquid water can penetrate interconnected pores and become retained within the porous network, Y-Warm’s predominantly closed cells restrict direct liquid-water penetration into the pore interiors. Instead, moisture interacts primarily with hydrophilic groups at the material surface and within the polymer matrix.
As a result, water is less likely to become deeply trapped within an interconnected porous network and can remain relatively accessible for subsequent transport and evaporation. This structural characteristic contributes to faster moisture release during the drying process.
Second, Y-Warm’s extremely high porosity (>96%) gives the material a very low overall density, with a surface density of only approximately 46 g/m². Combined with its ultra-thin structure, this means that only a small amount of material is present per unit area and the thermal mass of the material is correspondingly low.
More importantly, at a finished thickness of only 0.7 mm, the distance that moisture must travel from within the material to an evaporation surface is extremely short. This short transport pathway facilitates the rapid migration of moisture toward the surface, where it can subsequently evaporate into the surrounding air.
Third, Y-Warm’s rough surface morphology increases its effective surface area compared with a geometrically flat surface. Since evaporation is strongly influenced by the area available for mass transfer, this increased effective surface area can provide more sites for moisture exchange with the surrounding air.
The micrometer-scale surface morphology therefore contributes to the rapid release and evaporation of moisture, supporting Y-Warm’s quick-drying performance.
4.2 The Supporting Role of Temperature and Vapor-Pressure Gradients
Under actual wearing conditions, Y-Warm can experience different temperature and humidity conditions on its two sides. The inner side is exposed to the warm, humid microclimate close to the human body, while the outer side is generally exposed to cooler and, depending on environmental conditions, potentially drier ambient air.
Because Y-Warm limits heat transfer through the material, it can help maintain a relatively warm microclimate on the body-facing side. At the same time, differences in humidity and water-vapor partial pressure between the two sides of the material can provide a driving force for moisture transport.
Water molecules generated by perspiration can first interact with hydrophilic groups on the inner side of the material and subsequently migrate through the polymer matrix via molecular diffusion. When they reach the outer surface, they can be released into the surrounding environment and evaporate.
This creates an “adsorption–diffusion–release” pathway, driven primarily by differences in water-vapor concentration and partial pressure across the material. Together with Y-Warm’s ultra-thin cell walls and short diffusion pathways, this mechanism helps explain how the material can combine thermal insulation with moisture permeability and rapid drying.
V. Comparison with Traditional Insulation Materials
Traditional insulation materials, such as down and synthetic fiber batting, generally rely on a bulky, low-density fibrous structure to trap still air and reduce heat transfer. Their ability to manage moisture, meanwhile, depends largely on the structure of the fibers, the spaces between them, and the moisture-management characteristics of the constituent materials.
This creates an important design challenge. Increasing loft and thickness can improve thermal insulation, but greater material volume may also increase moisture-storage capacity and lengthen the pathways through which moisture must travel before reaching the surrounding environment. Once these materials become wet, their thermal and drying performance can therefore be affected.
Y-Warm employs a fundamentally different structural approach. Rather than relying primarily on a thick, lofted fibrous layer to trap air, it uses a predominantly closed-cell porous structure to suppress heat transfer within an extremely thin material. At the same time, hydrophilic functional groups incorporated into the polymer matrix facilitate the adsorption and molecular diffusion of water vapor.
In this way, thermal insulation and moisture transport are achieved through different but complementary mechanisms: the closed-cell structure contributes primarily to thermal resistance, while the hydrophilic polymer matrix provides a pathway for water-vapor transport.
This structural and molecular-level division of functions helps Y-Warm combine thermal insulation with moisture permeability without relying on the conventional strategy of increasing material thickness.
The difference is also evident in drying behavior. Hydrophilic natural fibers such as cotton can absorb substantial amounts of moisture into their internal fiber structure, and the absorbed water must subsequently migrate back toward the fiber surface before it can evaporate. This can prolong the drying process.
In Y-Warm, by contrast, the combination of an ultra-thin structure, nanoscale cell walls, short molecular diffusion pathways, and a large effective surface area enables moisture to reach the evaporation surface more rapidly. These characteristics contribute to its high evaporation rate and quick-drying performance.
Conclusion
Y-Warm’s exceptional moisture permeability and quick-drying capabilities are not the result of a single factor, but rather the product of the synergistic interaction of multiple factors: the physical properties of the closed-cell structure, the chemical properties of the hydrophilic groups, the diffusion advantages of the nanoscale thin walls, and the evaporation gains from the rough surface. A closed-cell rate of over 95% ensures that thermal insulation performance is not compromised by moisture-permeable channels; a porosity of over 96% results in extremely low density and heat capacity; and pore wall thicknesses ranging from 20 to 280 nanometers provide the optimal path for the efficient diffusion of water molecules. This integrated “structure–chemistry–surface” three-dimensional design philosophy makes Y-Warm a model of integrated thermal insulation, moisture permeability, and quick-drying functionality in the field of porous materials.