Filler: Product used to replace missing pigment before coloring

ByDr. Celestine (Certified Trichologist)

What is Filler?

Filler is a conditioning treatment that patches holes in damaged hair strands. It works by depositing proteins or other agents into the hair’s inner core to create a smooth surface. This process helps your hair absorb and hold onto color and moisture much more evenly.

Most people think fillers are just for deep conditioning. The surprising fact I share with my clients is that a filler can actually prevent your hair color from turning out patchy or fading too fast. It acts like a primer before you paint a wall, ensuring the color sticks uniformly.

How Filler Plugs the Porosity Problem

Your hair is like a sponge with tiny holes when it’s damaged. A filler product contains small molecules that slip into these gaps. It temporarily fills the empty spaces in the hair’s cortex, which is its inner layer.

Think of your hair strand like a road full of potholes. The filler is the asphalt that smooths everything over before you apply the topcoat of color. This creates an even foundation so the color doesn’t sink into some spots and skip over others.

I see this make a huge difference for clients who have bleached hair. Their high-porosity hair soaks up color unevenly without a filler, leading to a blotchy result. Using a filler first ensures the final color is vibrant and consistent from root to tip.

When Your Hair Desperately Needs a Filler

You need a filler when your hair feels gummy when wet or drinks up conditioner instantly. These are classic signs of high porosity, where the hair’s protective outer layer is compromised. The cuticle scales are lifted or missing, creating gaps.

If you have a combination of virgin hair and previously colored lengths, a filler is non-negotiable. The colored sections are more porous and will grab dye faster than the untouched roots. A filler equalizes the porosity across your entire head of hair.

In my clinic, about 80% of clients who complain of color fading too quickly actually have a porosity issue. They’re not using a filler, so the color molecules simply wash out of the damaged sections within a few weeks.

The Filler and Color Chemistry Connection

Hair color develops by opening the cuticle and depositing pigment inside the cortex. On damaged hair, the color developer works too aggressively on the weak spots. This can lead to over-processing and further damage in those areas.

A filler creates a more uniform surface for the color chemicals to act upon. Think of it like pre-treating a stained wooden table before you apply a light-colored paint. Without that base, the stain bleeds through and creates an uneven finish.

I never apply a demi-permanent color over severely damaged hair without a protein filler first. The color will grab too heavily on the damaged bits, creating a two-toned effect that looks artificial and splotchy.

Will It Work For You?

Yes

  • If your hair is chemically processed, bleached, or frequently heat-styled.
  • When you are making a major color change, especially going darker.
  • If your hair feels dry, spongy, and tangles easily when wet.

No

  • If your hair is healthy, low porosity, and has never been colored.
  • When you are using a temporary or direct dye that just coats the hair.
  • If you have scalp irritation, open wounds, or are allergic to common protein ingredients.

From My Experience

In my practice, I’ve developed a simple test to see if a client needs a filler. I take a single strand of their hair and gently stretch it while it’s wet. If it stretches like bubble gum and doesn’t spring back, that’s a clear sign the internal structure is compromised and needs filling.

Many clients are surprised when I explain that over-moisturizing damaged hair can make it worse. It’s like adding water to a crumbling brick wall—the structure is still weak. A protein-based filler rebuilds that internal scaffolding so the moisture you add afterward has something to hold onto.

The most dramatic transformations I see are when clients use a filler as part of their color correction journey. It’s the unsung hero that allows us to achieve even, lasting color on hair that was once considered too damaged to hold it. It truly bridges the gap between hair that is merely surviving and hair that is thriving.

Celestine Gitau is a Certified Trichologist (International Association of Trichologists – IAT), Trichology tutor, and experienced hair and scalp health specialist. She has extensive expertise in diagnosing, treating, and managing hair loss across all hair types, with a focus on afro-textured hair. Over her career, she has been involved in more than 450 hair transplant procedures and hundreds of advanced treatments including PRP therapy, nutritional supplementation, and stem cell applications. As a dedicated educator and blogger, she has authored numerous in-depth articles to raise awareness on hair and scalp health. Her work combines clinical experience, ongoing research, and a passion for patient education.
Note: The information shared is for educational purposes only and is not a substitute for professional medical advice. Always consult a qualified healthcare provider for personalized guidance.