This is flask liner paper that is used for 2 purposes for phosphate bonded invested flasks. The first purpose is to move water from the investment towards the top and bottom of the flasks by molecular cohesion transport. The second purpose is to create a cushion to handle the expansion of the silica investment material as it goes through it's alpha and beta phase expansion during the burnout cycle. This cushion prevents your mold from cracking during the extreme temperatures of the burnout cycle. It also makes cleaning the phosphate investment out of the mold after the casting process is complete by preventing it from sticking to the inside walls of the flasks. The paper is about 1/2 inch shorter than the flask so that you can have 1/4 inch top and bottom of the flask where the investment material does make contact to secure the invested mold in the flask during operations.