those scarf/hoods are knit at an extra loose guage to give them the stretch/contraction needed for the transition. I think fluffy yarn is probably used because it fills up the 'holes' of the very loose fabric and makes it look more solid.
Regular yarn might work but you will need to have a very open weave to achieve the same function. Hope that makes sense.
maybe a mohair type yarn would work for that.
here is 2 more links for another one, worked in regular yarn (different method).
this shows picture tutorial for that pattern.