Just wonder but...

Why is it bad to line your walls with tin foil, if growing indoors?

yes..use mylar...or better yet a can of flat white paint...foil is wrinkly and will cause hot spots.......also flat white paint will reflect more light than foil anyways.......don't use high gloss thinking it will be better either....flat white

Yep, the answer is hot spots. It's the same effect as using a magnifying glass to focus the sun on a point to make it heat up really quickly. In the case of your grow, it's obviously bad because you have no idea where the hot spots will end up and plus, you don't want anything burning in the first place.

Cuz it doesn't look cool, man!

Hahaha thanks for that info guys