Detachable collars are in the trend now accordingly to Urban. Strangely I thought I have seen them a few years ago in hmm think should be parco millennium walk carrying those japanese style collars or was it in Isetan that I seen it. The only thing that stop me from buying is the price.
Anyway for those contemplating it, maybe you can try making it. There you go.
http://www.ecouterre.com/make-a-detachable-collar-for-popping-over-your-sweater-diy-tutorial/
