The Under Armour Women's UA Tech Twist Crew Long Sleeve shirt ($30) is the perfect top for my outdoor workout classes because it keeps me warm on cooler days, but I never get too hot, even during the hardest parts of the workout. The fit is also ideal for functional movement: it's fitted so it doesn't get caught in equipment, but it's not too tight, so I feel like I can move around comfortably. Plus, the $30 is a steal compared to other competitors.