A MIPS bike helmet consists of a low-friction interlayer with elastic attachments between the EPS lining and the padding. It allows the helmet to move slightly (slide and rotate) in relation to the head to absorb the lateral and rotational forces involved in a fall. This is how helmets with and without MIPS differ; those without MIPS only absorb the blow through compression of the EPS lining. So if you want to be sure you're wearing a safe bike helmet, go for a MIPS bike helmet.