The ear phones do block all external noise,But only when you are listening to something. So, sound is blocked with the help of a high-powered dynamic speaker system that actually cuts off most of the noise. Testing this in the office I had to pull out the earphones every time someone was talking to me, that too only because I saw them trying to gain my attention.
The audio quality is really good,very loud but not create splitting to ear and lets you enjoy all types of music ,but this is not an audiophile headphone like the Momentum.
The best thing about the CX275s is the price. It comes at the price of Rs 2,990.