Stack the Volumizer weft on top of the 4-clip weft from your full set. It can be clipped in directly underneath the band. This means that you'll have double the thickness but will only need to clip in one weft still. See the video below.
Section off the bottom half of your hair and clip in your 4-clip Volumizer weft at the roots. Then, apply your Halo hair extensions as normal. If you have short hair, please click here for step-by-step instructions.