What type of antifreeze does the 2008 chevy impala use?

Your 2008 Chevrolet Impala should be filled with so called Orange antifreeze. You'll want to use A50/50 mix. The best thing to buy here is going to be Prestone DEX-COOL, part #AF860, which is sanctioned by GM, pre-diluted so You don't have to mess with finding distilled water, and runs about $17 for a gallon at Autozone. Consider that if You haven't had to previously add coolant, You might have a leak. The 3.5 and 3.9 engines, especially, have a known issue with the gaskets failing on the coolant crossover pipe (an aluminum casting connecting the front and rear heads of Your engine). If You smell coolant after running Your Impala, this is something to check; obviously, You should also be pro-active if You start seeing pooled coolant under Your engine and address it.