DIY portable 8x4 foot board

End product 

Foldable board made of 3 pieces of 3x 4 feet foam core boards: 

with 8.3 cm x4 feet strip trimmed off the width, the three taped together span 8 feet.

Foldable

Two faces: black or white

Packable

Portable

My foldable 4x8 board was mounted on a 3x6 board hybrid with a 4x6 board:

I brought it along just in case.

Event manager failed to come up with 4x8 board.

Three flip chart easels bound together with duct tape: 

3M hooks, twine: whatever it takes; 

it worked.

Addendum

In response to question on duct tape

I used 13 mm thick foam core board and very happy with it: 5 mm might work, but more flimsy: my 13 mm gives a good support.

Use fabric based 2 inch wide duct tape.

The duct tape has to be on the inside of the fold: imagine three pieces of foam core board : each three foot by two foot: name them A, B,C: and for easy reference consider they have different color on each face, one side black, one side white.

Assemble ABC in front of you, black face facing you: if you tape a

A and B together on the black surface,  they can fold upon each other. To Zfold, B must be taped  to C on the white surface. 

(If B and C are also taped on the black surface , then your device can not Z fold)