Getting to Know Your Hair: Diameter, Density, and Porosity

For many of us, our hair tends to be either our best friend or our worst enemy. All hair has the potential for being stunningly gorgeous, but if left to its own devices it can be nothing short of a stubborn mess. One of the most important things you can do to make sure your hair is always your friend and looks beautiful is to get to know it. In this first article of our two-part series on getting to know your hair, we’ll discuss the diameter, density, and porosity of hair.

Hair Diameter

When someone talks about having thick hair, that can mean one of a couple of different things. One thing they could be referring to is the diameter of their hair, or how thick the individual strands are. The thickness of the strands can impact how strong they are. Diameter is divided into three categories: fine, medium, and coarse. You can test diameter by holding a single strand of hair between your thumb and index finger. Coarse hair can be distinctly felt. Medium hair can be slightly felt between the fingers. Fine hair will barely be felt, if at all.

Hair diameter also plays a major role in how your hair responds to styling products and services. Fine hair tends to become weighed down more easily by heavy creams and oils, while coarse hair often benefits from richer moisturizing products that help smooth the hair cuticle and reduce frizz. Medium hair typically falls somewhere in between and can adapt well to a wider range of products.

It’s important to remember that hair diameter is not the same as hair density. You can have fine individual strands but still have a full head of hair, or you can have coarse strands with fewer hairs overall. Understanding your strand diameter can help you and your stylist choose the right products, treatments, and styling techniques to keep your hair looking and feeling its best.

Hair Density

The other thing someone might be referring to when talking about hair thickness is how dense their hair is, or how closely the strands are grouped together. A person who has more strands of hair is going to have hair that is more dense. This can impact the volume of your hair. Density is divided into three groups: thin, medium, and thick. It’s easy to tell how dense your hair is with a simple mirror test. Grab a large handful of hair and pull it to the side. You have thin hair density if you can easily see your scalp, medium density if you can partially see your scalp under your hair, and thick density if you can hardly see it.

Hair density affects much more than volume. It can influence which haircuts work best, how long it takes your hair to dry, and even how much product you should use. Those with higher-density hair often require more product to evenly distribute moisture, while those with lower-density hair typically benefit from lighter formulas that won’t leave the hair feeling heavy.

Knowing your hair density can also help set realistic styling expectations. For example, someone with low-density hair may create the appearance of fuller hair with layered cuts or volumizing products, while someone with high-density hair may prefer styles that remove bulk and make everyday styling more manageable. Understanding your density allows your stylist to personalize recommendations based on your hair’s natural characteristics.

Hair Porosity

Porosity refers to the hair’s ability to absorb and retain moisture. Because the correct level of moisture is important, knowing your hair’s porosity can help you choose and use products better. Again, a simple test can help you determine your hair’s porosity, which can be divided into high, normal, or low porosity. Pluck a single strand of hair and submerge it in a cup of water. If it sinks, your hair has high porosity. If it floats in the middle, it has normal porosity. If it floats on top of the water, it has low porosity.

Hair porosity is largely determined by the condition of the hair cuticle. Hair with low porosity has a tightly sealed cuticle that makes it more difficult for moisture to penetrate, while high-porosity hair has a more open cuticle that absorbs moisture quickly but also loses it just as easily. Hair that has been lightened, colored, chemically treated, or frequently heat styled often develops higher porosity over time.

Understanding your hair’s porosity can make choosing the right hair care routine much easier. Low-porosity hair generally responds well to lightweight products and gentle heat to help moisture absorb, while high-porosity hair often benefits from richer conditioners, leave-in treatments, and products designed to lock in hydration. By selecting products that match your hair’s porosity, you can improve manageability, reduce frizz, and maintain healthier-looking hair between salon visits.

If you want to have beautiful hair on a regular basis, you need to become intimately familiar with it. So much of how your hair looks is impacted by the products you use on it. The more you know about your hair, the better you’ll be able to choose the right products to get the results you want.

Learn More About Caring For Your Hair

Now that you’ve learned about the characteristics of your hair, let’s get more detailed with a guide for your specific hair type!

• A Deeper Dive Into Hair Types: Coily Hair
• A Deeper Dive Into Hair Types: Curly Hair
• A Deeper Dive into Hair Types: Straight Hair
• A Deeper Dive into Hair Types: Wavy Hair

We like to say that a great haircut is a work of art. Check out our hair design services to see how we can give you your own personal work of art today.