As someone who has ADHD and uses earplugs to study, I recommend using the classic foam style earplugs, because as far as I am aware, they are the only type that is allowed during the actual exam. That might have changed, but it definitely used to be he case. Also, if you find foam earplugs to be ineffective, make sure that you are using them right. Most people just cram them in their ears, but the proper way to insert them is to like squish/roll them up, insert them, and then let the foam expand back out.