Why is keratin a popular choice for hair extension bonds?

Keratin is a favored choice for hair extension bonds primarily because it closely resembles the natural structure of human hair. This similarity in composition allows for a more seamless and natural look when the extensions are applied, as the keratin bonds blend well with the existing hair. Additionally, since keratin is a protein that is a key component of both hair and nails, using it in extensions ensures compatibility with the natural hair's texture and strength. This makes the extensions less likely to cause damage or breakage to the natural hair while maintaining durability over time.

The other options, while they might address certain aspects of hair extensions, do not capture the essence of keratin's advantages in bonding. For instance, although it may be true that keratin bonds can be removed and some methods may be cost-effective, these factors are secondary to the primary reason for its popularity—its ability to mimic the natural structure of hair. Similarly, keratin itself does not add color to the extensions, as its role is strictly functional in terms of bonding rather than aesthetic in contributing color.