Eliyahu,  Right you are.  I've used pizza boxes a couple times and
they fit quite well.  They even come in different sizes -- how handy!

Our local shop sells pizzas as large as 30 inches diameter and as
small as 6 inches.  I turn them inside out so it doesn't say "Pizza"
on the outside.  When you tape them on the corners and sides, they
are quite strong.

And the nice thing is that you can get them for free by ordering a
pizza, they bring them right to your door, and you can enjoy the pizza
while you're packing the disks.  (I add a piece of Masonite, just in
case.)  What more could you ask.

Regards,
Craig Smith

P.S. By the way, they work particularly well for discs with melodies
like "William Tell" and "O Sole Mio"!

 [ Masonite is rather dry; may I have extra sauce with mine, please?  ;-)
 [ -- Robbie