I get it. You're standing at the counter, holding two tees that look almost identical, but one is a size up. You're about to board a flight to somewhere hot, and you want to look good without sweating through your shirt by noon. So which one do you grab?

Here's the short answer: it depends on how you travel. If you're a backpacker who lives out of a carry-on, regular fit is your friend. If you're more of a 'throw a duffel in the trunk' type and want maximum airflow, oversized is tempting. But there's more to it than just the fit.