Summarised_Solution:
Pink foam is OK but not really intended for this purpose.
Possibly the best deal of all is from DESCO !!!
Their cheapest per area suitable material is this = Desco 12150 - 24" x 36" x 1/8" high density at $US7.14. That's a magical ~$1.20/ft^2 and you can use 2 layers to get 1/4" etc. Multilayers is never quite the same but is good enough. Shipping cost unknown. May make or break order.
The pink foam material is usually used for shipping as a wrapper or outer layer . It may not be measurably surcace conductive. It may well do the job "well enough" but you can probably do better.
Idea is high density conductive foam that is thick enough that IC pins do not push right through. Thinner works as well but the IC's stand off the surface and you don't get the same seating feel when pressing them in.
RS are not known for their low prices.
Heree they have 305 mm x 305mm x 6mm (1 square foot x 1/4 inch) of conductive foam for $NZ2.78
RS550-066. Lower in $US hopefully. NB: This is low desnisty foam. Others below probably hi density. Low density works OK, dies sooner, need to be sure it always contacts all pins as it gets older but should be a good starting material.
Many related products. Good site. Dearer than RS but high density. eg $22.32/6 square feet x 1/4 " or 3.72 / ft^2. here Texas HQ.
Hmmm. RS USA may not have the NZ foam. RS India does.
RS US have this
DESCO 12250 24" x 36" x 1/4" $US23.66.
Thy also have 3/8" thick version for $41.46 here.
8 sellers here with RS being cheapest :-(.
Digikey list it and other versions but no stock and dearer here
Desco sell it theselves for around $25 here
BUT they do a range of closely related products here
DESCO !!!
And probably best of all for you is this
Desco 12150 - 24" x 36" x 1/8" high density at $US7.14.
The 1/8" is annoying, but at ~ $1.20/ft^2 it's excellent.
You can use 2 layers to get 1/4" for $2.40/ft^2 and 3 layers to ... :-).
Multilayers is never quite the same but is good enough.
Shipping cost unknown. May make or break order.
Dow on conductive foams. Reference only but very ionteresting here
Foam. Jameco. Too dear. Reference only at $US8/ft^2 here
Some excellent idea starters for conductive materials here
As anti-static foam isn't reusable, if the laptop has no exposed electrical connections, and the threat you're guarding against is ESD damage to the laptop, and the cost of the foam is small compared to that of the laptop, then use the most conductive foam you can find, namely cushion grade conductive foam.
(I feel faintly embarrassed posting this. You should really get credit for this answer.)
Best Answer
Try hooking alligator clips & multimeter leads to the bag.
Good anti-static bags should have some measurable conductivity (i.e. resistance less than infinity/err on your meter).