Preserving Vintage Boxes

Dear Donia,

How do I maintain the shape of empty vintage Christmas boxes? 

Vintage Christmas box

Q. Dear Donia,

I have a number of pretty vintage Christmas boxes (basically card-stock cardboard boxes with Christmas paper glued to the surface made into a box). I would guess that they are from the 1940s based on the style of decoration on the paper. Any empty box stored for a while tends to become slightly misshapen. I had an idea that I might ask my carpenter son to make me pieces of some light-weight softwood to hold the shape of the boxes. However, I think the lignin in the wood might cause them to deteriorate faster so I'm wondering about some other substance I could use to fill the boxes and help them hold their shape. Would styrofoam work, or would it also degrade the
material? Thank you for any suggestions you might have. Kind regards, Carol

A. Dear Carol,

I bet your boxes are such fun to have out around Christmas! 
You are correct that wood would be damaging, as would standard Styrofoam—both of which would off-gas harmful materials that would deteriorate the boxes and wrapping paper over time.
To help hold the share of the boxes, you could use a foam material called Ethafoam which is chemically stable and would not off-gas. 
If the Ethafoam is too costly for you, you could make your other options safer by wrapping the wood or Styrofoam with a couple of layers of tinfoil and then in some cotton muslin so it doesn't look to bad.from the outside.  The tin foil will act as a vapor barrier to prevent the off-gassed materials to damage the boxes and the cotton muslin will be a softer material to have in contact with the paper.
I hope this helps and that your Christmas boxes will hold their shape better in the future!