Scientists have found one odd exception to the research on clothing comfort and cognitive performance: helmets. Unlike shirts and pants, uncomfortable helmets don't decrease auditory and visual vigilance—the kind of attention that you need when, say, you're cycling in Manhattan. Thank goodness for that result, no? Otherwise, your bike helmet might actually make you more likely to crash. So what's so special about helmets, anyway? The researchers aren't sure. It could simply be in that the kinds of situations in which we wear helmets—cycling, sky-diving, mosh pits—the other incoming stimuli are so visually, auditorily, and kinesthetically intense that they simply drown out the cognitive load of the tightness of the helmet. Exams, on the other hand, while potentially stressful and important to your future, don't quite demand your attention the way that jumping out of an airplane does.
To summarize: If you're heading into an exam, arrive in your snuggie, shake hands with the prof, and, if you think it'll help you out, don't hesitate to wear that tin-foil hat.