what is waterboard?

I checked out a book at a library a few days back titled "Custom Auto Interiors" by Don Taylor and Ron "The Stitcher" Mangus.  The book has a date of 1998.  So far, Ive read through certain sections that interested me, which caused me to cross "Waterboard". 

They describe it as a waterproof panelboard.  In the 1930's to 1950's, it was used for all paneling - OEM and aftermarket.  They claim its greatest advantage was the ability to be sewn.  Its disadvantage was, that is was really not very waterproof.  After several exposures to water, it would warp badly.

The illustrations and pictorials in this book shows them several times using it to form underdash panels and headliner sections. 

Is this waterboard just another name, or old school name for something we already know as some other name?  Is it just a thinner Masonite like material?

Thanks.

Heh, is this for real?  Nobody?!    0 out of 32, wow!

Well, I guess since nobody knows, it means were young.

Almost forgot about this thread....

Well, I know what waferboard is, but according to the book I had referenced above, it looks more like brown posterboard but thicker, more to the likes of Masonite...but its neither.

Im just going to accept the fact that its the lesser of our modern methods and just continue doing what I do, because posterboard is too weak, and Masonite is way thicker that this "waterboard", and both are worthless in comparison to "waterboard".

I have one other person to ask, an upholsterer, Ill share his input.  Thanks for the replies.