What is Hair Elasticity?

Hair is a protein fiber with a cylindrical structure comprising tiny microfibers that are packed in a well-organized shape in the cortex. Applying force to a damp hair strand causes it to stretch and become longer. This is due to the expansion of microfibers, which act like springs within the hair cortex.

According to experimental data, wet hair that has not been chemically treated can stretch up to 30% of its original length. The hair will return to its original length once it is dry. This is known as hair elasticity.

The level of elasticity in hair varies depending on ethnicity and hair type. Furthermore, hair that has undergone chemical treatments or modifications has different elasticity compared to untreated hair. This is because elasticity is determined by the integrity of the inner structure, which is formed by tightly bonded microfibers in the hair cortex.

It has been experimentally proven that hair fibers that have a nicely packed and bonded cortex possess higher elasticity, while fibers that are damaged with broken microfibers possess lower elasticity.

Hair fibers that have been subjected to bleaching, chemical processing, or UV damage have been measured to possess lower elasticity than natural, virgin hair fibers. The decrease in elasticity can be linked to the breaking of disulfide bonds in the chemically processed hair fibers.^6–7 

When you apply excessive force and stretch your hair beyond 30%, it becomes weaker and its structure gets damaged. There is a possibility that your hair may not completely recover and return to its original length.

Excessive force can lead to hair breakage, which is measured experimentally as the “breakage load” and is a crucial parameter for determining the strength of a hair strand.

Hair Elasticity and Porosity

Assessing the mechanical strength of hair fiber requires a fundamental tool known as elasticity. It demonstrates the ability of hair fiber to return or bounce back to its original shape or length after being stretched or twisted.

To put it simply, elasticity refers to how resistant hair fibers are to being bent out of shape when force is applied. It’s an important factor studied in the scientific literature.^1-4

Elasticity is directly related to the level of hair damage and porosity.⁵ Healthier and stronger hair fibers have higher elasticity, while damaged hair fibers tend to have lower elasticity.

Elasticity: Stress, Strain, Young’s Modulus: Some Basic Terms

In physics, elasticity refers to a material’s ability to revert to its original shape after being subjected to stretching or misshaping by an applied force. This is determined by the ratio of stress (the amount of force per unit area) to strain (the extent of deformation, distance, or work done) resulting from the force.

Using hair fiber as an example, stress refers to the amount of force used to stretch the hair fiber, while strain describes the resulting increase in fiber length. The relationship between stress and strain is known as fiber elasticity.

The mathematical relationship defining these terms is given here:

E = Stress / Strain

E represents the elasticity, which is also known as Young’s modulus.

Measuring Elasticity

The measurement of elasticity involves measuring the increase in length resulting from an applied force. Mechanical analyzers can be used to measure both force and deformation in hair fibers.

Hair scientists use advanced technology like the Dynamic Mechanical Analyzer to the mechanical properties of a single hair fiber, including its strength, breakage load, and elasticity under specific humidity levels.

Additionally, they use combing machines to assess the ease of combing and friction of both dry and wet hair fibers.

How to Test Hair Elasticity

You can easily test the elasticity of your hair yourself at home or a salon with a professional.

At Home

Is it possible to check the elasticity of our hair at home? Yes, we can do a simple experiment that will help us get an idea about our hair fiber’s elasticity.

Put a mark on the scale of 30% and start stretching the hair fiber very gently by pulling it with your fingers. (Let’s say hair length was 10cm, its 30% would be 13cm). Stretch it to the 30% mark, hold it there for 10 seconds, and then release it. Let it come back to its original length and dry it out. 

1. Grab a single hair strand and wet it with room-temperature tap water.
2. Gently remove excess water with a paper towel.
3. Place the hair strand on a sheet of paper and position a measuring tape alongside the side of the hair. Then, measure the length.
4. Put a mark on the measuring tape at the 30% mark.
5. Start stretching the hair strand gently by pulling it with your fingers. Stretch it to the 30% mark, and hold it there for 10 seconds.
6. Then, release and allow it to return to its original length before drying it out.
7. Let’s say your hair length was 10cm, its 30% would be 13cm. The hair should return to its original length, and if it does not then it means that the elasticity of your hair is low.

You may observe the following possibilities in this experiment:

● Your hair returns to its original length after completely drying, this indicates that your hair is healthy and has good elasticity.

●Your hair doesn’t return to its original length when it dries, it may have low-to-medium elasticity.

●Your hair broke while being stretched, indicating that it is weak, damaged, and has low elasticity.

You can also estimate the elasticity of hair fibers by measuring the final length after stretching and calculating the ratio between the original length and the length after stretching.

At a Salon

If you want to check the elasticity of your hair at a professional level, then it is best to go to a salon for the assessment. Professionals can provide tips and products that are specifically designed to increase the elasticity of your hair.

They may use the following signs that indicate good hair elasticity:

Hair that can be stretched by up to 25–30% of its original length and then quickly returns to the same shape.

• No breakage when combing or brushing.
• No split ends or brittle strands.
• A pleasant bounce and body in the hair.
• Shine.
• Smooth cuticles.

If your hair feels a little rough, it means it needs moisture. On the other hand, if your hair is moisturized, it will have a smooth and silky texture. A combination of both —moisture and elasticity— is ideal for healthy hair.

Factors that Lower the Hair’s Elasticity

The elasticity of hair depends on its structural integrity, which has two parts: the outer cuticle layer and the inner cortex.

The cortex is the main part of the hair and gives it its mechanical strength. If the cuticle layer or cortex is damaged, the hair’s structure, tensile strength, and elasticity are affected.

Here are some factors that may cause damage to fiber and decrease its elasticity.

How to Recover or Improve Hair’s Elasticity

Elastic hair is healthy and easy to style, groom, and manage. It’s crucial to preserve hair elasticity and restore it after undergoing harsh chemical or physical treatments.

Hair elasticity can be recovered or improved by using specifically designed hair care formulations that are designed to strengthen the hair fiber. Adapting to a hair care regimen can also help the recovery of hair elasticity.

Here are some simple steps to help you regain the elasticity of your fiber.

1. Keep your hair clean and hygienic 

To prevent additional harm to the hair, it’s best to use a shampoo without sulfates. Sulfates are known to dissolve proteins from the hair shaft. 

2. Hydration

The moisture level of your hair is important for its health and quality. Hair that is dry and brittle tends to lose its elasticity and becomes tough, making it harder to manage and style. To maintain a healthy water level of your hair fiber, it’s recommended that you regularly use a hydrating conditioner, leave-in conditioner, and hair treatment mask.

3. Conditioning

Applying certain ingredients, such as cationic hair detanglers, conditioning polymers, and proteins, to the surface of hair can increase its elasticity. The polymers, in particular, create a thin layer over the hair and change its strength by penetrating the hair structure.

Protein treatments like hydrolyzed wheat protein work similarly by allowing small protein fragments to enter the hair surface and penetrate deep into the structure. This helps fill empty spaces in the cortex caused by chemical treatments, restoring the hair fiber’s mechanical strength and boosting its elasticity.8 Therefore, regular conditioning and deep conditioning treatments are crucial for maintaining healthy hair.

4. Minimize the harm from daily hair combing and brushing

To make combing and brushing easier and protect the strength of your hair, use a combing detangler or leave-in conditioner that contains detangling agents, emollients, and hydrating ingredients.