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Glass Transition Temperature vs. Melting Temperature: What's the Difference?

Edited by Aimie Carlson || By Janet White || Published on December 1, 2023
Glass transition temperature is the temperature at which amorphous materials become rubbery from rigid, while melting temperature is the point at which a solid becomes a liquid.

Key Differences

Glass transition temperature (Tg) is the temperature range at which polymers or amorphous solids transition from a hard, glassy state to a soft, rubbery state. Melting temperature (Tm), on the other hand, is the specific temperature at which a crystalline solid turns into a liquid.
Tg does not involve a phase change; instead, it marks a change in the physical properties of the material. In contrast, Tm is the temperature at which a material undergoes a first-order phase transition from solid to liquid.
At the glass transition temperature, the material remains amorphous and disordered, becoming more flexible. Melting temperature is characterized by a structural breakdown, leading to a change from an ordered solid to a disordered liquid.
Tg is typically lower than Tm for a given material and is particularly significant in polymer science. Tm is a fundamental property in materials science, indicating the temperature at which a substance can no longer maintain its solid crystal structure.
The glass transition temperature is influenced by factors like molecular weight and plasticizer content, while the melting temperature is determined by intermolecular forces and crystal structure.

Comparison Chart

Type of Transition

Physical change in amorphous materials
Phase change in crystalline solids

Change in State

From rigid to rubbery, no phase change
From solid to liquid, a phase change

Material Structure

Amorphous and disordered
Crystalline and ordered

Influence Factors

Molecular weight, plasticizer content
Intermolecular forces, crystal structure

Importance in Science

Critical in polymer science
Fundamental in materials science

Glass Transition Temperature and Melting Temperature Definitions

Glass Transition Temperature

Tg is influenced by the polymer's composition and additives.
Adding a plasticizer lowered the glass transition temperature of the polymer.

Melting Temperature

Tm is determined by the substance’s intermolecular forces.
The high melting temperature of diamond is due to its strong covalent bonds.

Glass Transition Temperature

It represents a change in the mechanical properties of polymers.
At its glass transition temperature, the polymer became more pliable.

Melting Temperature

Melting temperature varies widely among different materials.
The melting temperature of iron is much higher than that of aluminum.

Glass Transition Temperature

This temperature is key in determining polymer processing temperatures.
The glass transition temperature guided the temperature settings for molding the polymer.

Melting Temperature

Tm is the temperature at which a solid becomes a liquid.
The melting temperature of ice is 0°C.

Glass Transition Temperature

Tg is the temperature range where amorphous materials soften.
The glass transition temperature of this polymer is crucial for its application in flexible electronics.

Melting Temperature

It signifies a first-order phase transition in a material.
At its melting temperature, the metal transitioned from solid to liquid.

Glass Transition Temperature

Tg indicates when a material transitions from rigid to rubbery.
The glass transition temperature affects the material's use in high-temperature environments.

Melting Temperature

This temperature is critical in understanding a material's heat resistance.
Knowing the melting temperature helps in selecting materials for high-heat applications.


What does melting temperature indicate?

The specific temperature at which a solid turns to liquid.

Is glass transition temperature a phase change?

No, it's a change in physical properties, not a phase change.

What is the glass transition temperature?

The temperature range where amorphous materials become flexible.

Are all materials characterized by a glass transition temperature?

No, only amorphous materials like polymers exhibit Tg.

How is glass transition temperature measured?

Typically measured using differential scanning calorimetry.

Does the glass transition temperature affect material strength?

Yes, it influences mechanical properties like flexibility and toughness.

Does melting temperature vary with pressure?

Yes, it can change under different pressure conditions.

Can melting temperature be altered?

It can be influenced by factors like alloying in metals.

Do plastics have a glass transition temperature?

Yes, it's a key property for understanding plastic behavior.

Is melting temperature important in alloy design?

Absolutely, it's critical in determining alloy properties.

How does melting temperature relate to material purity?

Higher purity often leads to a more consistent melting temperature.

Can two materials have the same glass transition temperature?

Yes, but it usually depends on their chemical structure and composition.

Is melting temperature the same for all samples of a material?

Generally, yes, unless impurities or structural differences exist.

Does melting temperature affect welding processes?

Yes, it's crucial for selecting appropriate welding temperatures.

Is glass transition temperature relevant in 3D printing?

Yes, it impacts the printing temperature and material properties.

How does humidity affect glass transition temperature?

It can lower Tg in some hygroscopic materials.

Does color affect glass transition temperature?

Not directly, but additives that change color can influence Tg.

Does melting temperature determine a material’s suitability for high-temperature applications?

Yes, it helps in selecting materials that can withstand high temperatures.

Is melting temperature a factor in cooking?

Yes, especially for ingredients like chocolate or butter.

Can melting temperature be calculated theoretically?

Yes, using thermodynamic principles and molecular data.
About Author
Written by
Janet White
Janet White has been an esteemed writer and blogger for Difference Wiki. Holding a Master's degree in Science and Medical Journalism from the prestigious Boston University, she has consistently demonstrated her expertise and passion for her field. When she's not immersed in her work, Janet relishes her time exercising, delving into a good book, and cherishing moments with friends and family.
Edited by
Aimie Carlson
Aimie Carlson, holding a master's degree in English literature, is a fervent English language enthusiast. She lends her writing talents to Difference Wiki, a prominent website that specializes in comparisons, offering readers insightful analyses that both captivate and inform.

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