Substituting freezer paper for parchment paper I am making a brisket and the recipe calls for coating the meat with a tomato-based rub, which means I can't simply cover with foil... that would leave an unsavory taste in the rub because the aluminum would react with the tomato paste.  The recipe suggested parchment paper between the brisket and the foil; I am cooking at 200 degrees F for eight hours.

I read somewhere that parchment paper is sometimes coated with silicone; however, I also see that it's more than twice as expensive as freezer paper... locally I can buy 75 sqft of generic freezer paper for $2.50, but only 30 sqft of the same generic distributor's parchment paper is $2.68.


Is there a good reason why I can't substitute freezer paper for this
application (chemicals side facing the foil, of course)
Also, what kind of cooking situations is parchment paper best-suited for?
Parchment paper is not paper coated with silicon. It's actually paper that's been run through sulfuric acid, leaving it just a really thick matrix of cellulose. Long story short, extremely thick paper without the wood pulp.

Freezer paper is normal paper with wax applied to one side. I wouldn't use it for anything involving heat, as you'd end up eating the petroleum-enriched waxy bit in your food, and the paper might light on fire.

Parchment is used as a spill-proof surface in baking. Additionally, you can wrap foods in parchment (a technique known as cooking en papillote) and stick them in the oven, which effectively steams them in their own juices, so no flavor is lost. Salmon and vegetables are exceptionally delicious this way.