Katie's previous short cut was just long enough on top to hide the bonds where extensions are sealed onto small, underlying sections of natural hair, giving her a full head of thick, glossy locks that look truly amazing.
And while we're hoping she sticks with the new look, we have to note that extensions do require commitment.
You have to be careful brushing and de-knotting hair – too much tugging can loosen the bonds.
And styling hair can be difficult – you can't use heated appliances on synthetic extensions and even with those made from real hair, you have to avoid the bonds to stop them melting.
So Katie would have had to have used Velcro or bendy rollers to create that lovely wavy texture that wowed the crowds in Japan.
Once in – and taking three or four hours to apply, the initial cost runs into hundreds of pounds – extensions need 'maintaining' every three or months, which means replacing those that have loosened or fallen out.
If you have fine hair, extensions may not be for you, warns Daniel Galvin's top stylist, Lino Carbosiero. The weight of the extensions can cause tension at the root which could result in permanent damage to your own hair.