How to replace cushion filling on Eames Lounge Chair  

You can't really put new innards in without
cutting the tufting threads but they're easy enough to redo. You will need a long tufting needle and some tufting cord, both of which you can get online or at Joann Fabrics.

Thanks for the advice; it...
Thanks for the advice; it doesn't sound too hard, so hopefully I won't screw it up. As a side note, so far I've noticed at least 5 types of fasteners on the backings of the cushions for the 670's over the years. The first series had fasteners that look like bow ties. Later on, they had the kind where they attached the tufting cord to an 1" long silver tube which would go through one of the little holes on the backing and then perpendicularly secure the button against the backing. In fact, personally I find the silver tube to make the most sense because you can remove and put on easily. After that they've gone from white round fasteners to black round ones. I believe the latest productions have some sort of silver round ones. Am I missing other kinds?

Mine (2011) has black tape on...
Mine (2011) has black tape on the back of the cushions over whatever's holding the buttons on.

Cushion fasteners
Yeah, I peeled off the black tape on my 2010 production to look at the round fastener and it's a silver round thing. Does anyone know if the fasteners indicate any production year or series? Just to be anal about originality, I have a seat cushion from the 60's with a missing white round fastener although the the seat button stuck on pretty well and I want to see if I can find an exact white round one to replace it with. Any leads?

You might try contacting the ...
You might try contacting the eamesdesigns.com site that Daniel Ostroff runs. If anybody would know such fine details as the usually hidden fasteners, it would be him. Another would be to try to contact Alfie Hume who does a ton of 670/671 repairs.