Every winter, a “silent competition” plays out in the fashion world. On one side are bulky down jackets built around the principle that warmth comes first; on the other are lightweight garments attempting to balance style and comfort with protection from the cold. Meanwhile, materials engineers are asking a more fundamental question:
Why must warmth depend on thickness?
In recent years, a new thermal insulation material known as Y-Warm has offered a different approach. At just 0.7 mm thick, the material can increase perceived warmth by approximately 10°C under specified test conditions, while achieving a thermal conductivity comparable to that of aerogel.
To understand why such a thin material can provide effective insulation, it is first necessary to examine how the human body loses heat.
Heat is transferred from the body to the surrounding environment through three primary mechanisms: conduction, convection, and radiation. The fundamental purpose of thermal insulation in clothing is therefore straightforward: to reduce the rate of heat loss through these three pathways as much as possible.
For centuries, one of the most effective ways to achieve this has been equally simple: trap still air.
Conduction: Heat is transferred through direct contact. When you touch a cold metal railing, for example, heat flows from your warmer hand into the colder material. The rate of this transfer depends largely on thermal conductivity—the lower the thermal conductivity, the more slowly heat is transferred.
Convection: Moving air carries heat away from the body's surface. This is why cold wind makes the temperature feel significantly lower: it continuously disrupts and removes the thin layer of warm air surrounding the skin.
Radiation: The human body continuously emits thermal radiation, primarily in the infrared range. Even in still air, with little or no convective heat loss, radiative heat transfer continues.
Air has a thermal conductivity of approximately 0.025 W/(m·K) under typical conditions, making still air an effective thermal insulator. This explains the basic principle behind many traditional insulation materials—including down, cotton, wool, and synthetic fiberfill. Their structures create countless small spaces that trap air and suppress heat transfer.
This, however, creates a longstanding challenge in thermal insulation design:
To trap more air, conventional materials generally require more internal void space—and creating more void space usually means increasing thickness and loft.
I. Why “Thicker Means Warmer” Became the Conventional Rule
The clothing industry commonly uses the clo as a unit of thermal insulation. One clo corresponds to approximately 0.155 m²·K/W and is traditionally associated with the insulation required to maintain thermal comfort for a resting person under standardized indoor conditions.
For conventional fibrous insulation materials, thermal resistance generally increases with thickness, provided that the material maintains its loft and trapped-air structure.
This relationship explains why winter garments designed for extremely cold conditions are often bulky. A high-performance down jacket, for example, relies on a substantial volume of lofted down to create a thick layer of trapped air around the body.
If greater insulation is required, the conventional solution is usually straightforward: increase the amount and thickness of the insulating layer.
For generations, staying warm in extreme cold has therefore often meant accepting additional bulk and weight.
But does insulation always have to work this way?
II. Aerogel: Exceptional Insulation, but with Practical Limitations
Aerogel, first developed in 1931, is one of the best-known classes of nanoporous thermal insulation materials.
Silica aerogels can achieve extremely high porosity and exceptionally low thermal conductivity. Depending on their composition, structure, density, and testing conditions, certain aerogels can reach thermal conductivity values in the range of approximately 0.012–0.018 W/(m·K).
Their remarkable thermal performance has led to applications in fields ranging from aerospace and industrial insulation to specialized protective equipment.
The principle is clear: instead of relying solely on a thick fibrous layer to trap air, aerogel creates an extremely fine porous network that suppresses heat transfer at a much smaller structural scale.
However, conventional silica aerogel also has an important limitation: brittleness.
Its rigid inorganic network can fracture under bending, compression, or repeated mechanical stress. Pure aerogel may crack or generate particles, making direct use in flexible, repeatedly deformed products such as everyday apparel difficult.
This creates another materials-science challenge:
Can the thermal advantages of nanoporous structures be retained while overcoming their inherent mechanical limitations?
III. Y-Warm’s Approach: A Flexible Closed-Cell Porous Structure
Y-Warm takes a different structural approach by using functional polymers to create a flexible, nano-engineered closed-cell insulation structure.
Instead of relying on a rigid inorganic scaffold, the material combines extremely thin pore walls with non-interconnected cells within a flexible polymer framework. This allows Y-Warm to maintain an ultra-thin form while remaining soft enough for integration into textile products.
Three structural characteristics are particularly important to its thermal performance.
1. Closed-Cell Structure
Porous materials can generally be divided into open-cell and closed-cell structures.
In an open-cell material, neighboring pores are interconnected, allowing gases or liquids to move through the internal structure. In a closed-cell material, by contrast, individual pores are largely isolated from one another.
Y-Warm employs a closed-cell structure in which air is confined within numerous independent microscopic chambers.
By restricting internal air movement, this structure helps suppress convective heat transfer within the material.
In other words, rather than relying on a thick, lofted fiber network to hold large volumes of air, Y-Warm uses a much finer cellular structure to immobilize air within an extremely thin layer.
2. Ultra-Thin Pore Walls
According to scanning electron microscopy (SEM) and nano-CT structural data, Y-Warm features pore walls approximately 20–280 nanometers thick, with pore diameters ranging from approximately 30 to 190 micrometers.
This highly porous architecture reduces the amount of solid material available to conduct heat.
Because heat transfer through the solid phase depends partly on the continuity and geometry of the solid framework, minimizing the dimensions of the pore walls can help reduce solid-phase thermal conduction while preserving the structural integrity of the material.
The result is a material that combines an extremely thin physical profile with a high degree of internal porosity.
3. Flexible Polymer Framework
This is one of the most important differences between Y-Warm and conventional silica aerogel.
Whereas silica aerogel relies on a rigid inorganic network, Y-Warm uses a flexible polymer framework designed to withstand bending and deformation.
This structural difference addresses the brittleness problem at the material level.
As a result, Y-Warm can be cut, sewn, and quilted for integration into apparel and other textile products. It can also withstand machine washing at room temperature under appropriate care conditions.
Beyond thermal insulation, Y-Warm incorporates hydrophilic functional groups that contribute to moisture absorption and moisture-vapor management. Its structural and surface characteristics also support rapid moisture evaporation and high infrared emissivity, giving the material additional moisture-management and far-infrared properties.
Together, these characteristics allow Y-Warm to address a challenge that has long confronted thermal apparel:
How can high thermal efficiency, low thickness, flexibility, and moisture management be integrated into a single material?
In Closing
From the use of natural fibers thousands of years ago to today's ability to engineer porous structures at microscopic and nanoscopic scales, the fundamental principle of thermal insulation has remained unchanged:
Reduce the rate of heat transfer.
What has changed is the scale at which engineers can control that process.
Traditional insulation relies primarily on thickness and loft to trap still air. Aerogel demonstrated that highly engineered nanoporous structures could achieve extraordinary thermal performance with far less material thickness, but its brittleness has limited its use in applications requiring flexibility and repeated deformation.
Y-Warm represents another approach: using a flexible, closed-cell porous structure to control heat transfer within an ultra-thin material.
The significance of the 0.7-millimeter structure therefore lies not simply in making insulation thinner. It points toward a broader shift in thermal-material design—from relying predominantly on bulk and loft to engineering structure and thermal efficiency at increasingly smaller scales.
For the apparel industry, this could open new possibilities for winter clothing that no longer has to choose between warmth and lightweight design, thermal performance and flexibility, or insulation and comfort.