Concept Explanation: Why Cotton Clothes are Comfortable in Summer

During summer, our body sweats to cool down through evaporation. The type of fabric we wear affects how efficiently this sweat evaporates, influencing our comfort.

Step 1: Understand Sweat Evaporation

Sweat absorbs heat from our body to evaporate, providing a cooling effect. The rate of evaporation depends on factors like air flow and the fabric's ability to absorb and release moisture.

Step 2: Fabric Properties Matter

Different fabrics have different properties:

• Silk: Smooth but less absorbent; sweat may not evaporate quickly.
• Leather: Non-porous and hot; traps heat and moisture, causing discomfort.
• Cotton: Highly absorbent and breathable; allows sweat to evaporate easily.
• Rayon: Semi-synthetic; absorbent but may not be as breathable as cotton.

Step 3: Why Cotton is Best

Cotton fibers have a natural ability to absorb moisture (hygroscopic). They soak up sweat and allow it to evaporate due to good air permeability. This enhances the cooling effect and keeps the skin dry.

The comfort can be related to the evaporation rate, which is higher for breathable fabrics. The heat absorbed during evaporation is given by:

where $Q$ is the heat absorbed, $m$ is the mass of sweat evaporated, and $L_v$ is the latent heat of vaporization. Cotton facilitates this process effectively.

Step 4: Compare with Other Options

Leather and silk are less suitable because they do not absorb sweat well and may cause stickiness or overheating. Rayon is better than synthetic fabrics but still not as optimal as cotton due to lower breathability in some cases.

Final Answer

Cotton clothes are the most comfortable in summer because they are highly absorbent, breathable, and promote efficient evaporation of sweat, keeping the body cool and dry.

Related Topics

• Heat Transfer: Conduction, convection, and evaporation.
• Material Science: Properties of natural vs. synthetic fibers.
• Human Physiology: How the body regulates temperature through sweating.

Key Formulae and Theory

Latent Heat of Vaporization:

where $Q$ is the heat absorbed, $m$ is the mass of liquid evaporated, and $L_v$ is the latent heat of vaporization (for water, approximately 2260 kJ/kg).

Breathability: Measured by a fabric's moisture vapor transmission rate (MVTR). Higher MVTR means better evaporation and cooling.

Hygroscopicity: The ability of a material to absorb moisture from the air. Cotton can absorb up to 25% of its weight in water without feeling wet.