The answer to this lies in the type of hair extensions you get and the skill of your hair extension stylist. The short answer is that all bonds, if placed correctly and color matched correctly, should not be visible.
Here are some other considerations for making sure the bonds are not visible when getting hair extensions:
How do you wear your hair?
If a stylist does not ask about how you wear your hair, down and up, then it is a good bet that you will be able to see some of the bonds when wearing certain styles, because the placement of the hair extensions will not take your styles into account.
Match the Hair Extension Color to Your Base Color
Additionally, matching the color of your base color, not your end color, when doing microbead hair extensions will hide the bond.
The Best Hair Extension Bond
By far the best bond I have found is the fusion hair extension bond with the system volume Balmain hair extensions. The photo on this page shows how the bond is super small and clear so that it takes on the color of your hair, not the clear color that can sometimes appear like Elmer's glue. ( Learn more about Balmain » )
This is just tip of the iceberg when it comes to hair extensions, but just a quick aside I thought I would share after doing a beautiful set of system volume fusion hair extensions today!