Confused about UK packaging.

[Sundayboy]

I am sorry if this has been raised before on here. I have attempted to read through all posts before posting, but my question has not been answered. I am wanting to complete my UK release boxsets. I am aware that the current volumes are all released in the plastic version, but from what volume did they stop releasing the cardboard cases. My volumes 1 2 and 3 are all cardboard with inner thin cases. Did this change from volume 4? Many thanks in advance...

[Screwbaiter]

Yep. Volume 4 onwards was produced in the plastic.
I had been really looking forward to which characters would be featured on each individual cover as the series went on, but alas, too expensive for production.