MIPS stands for Multi-directional Impact Protection System. The MIPS technology was developed, and is owned, by a Swedish company who license it to helmet manufacturers. You will normally see the yellow MIPS logo on the back or side of helmet that use the system.
More and more cycle helmet manufacturers are using the MIPS system. It is now standard on almost all Bontrager helmets, Specialized are moving into MIPS in a big way and other manufacturers including Giro and Bell are also using MIPS.
What does MIPS do?
Standard bike helmets are built out of a polystyrene shell. When there is an impact the force is absorbed by that shell breaking apart. In a MIPS helmet there is a liner which is in contact with your head and will move independently from the outer shell when there is an impact. This allows some of the force of the impact to be absorbed before the polystyrene shell takes the hit and reduces the shock to the brain. MIPS works best in angled impacts which is how many real world crashes happen. Traditionally helmets have been designed for direct, head on, impacts so MIPS is argued to provide a safer helmet in real world conditions.
The MIPS system typically adds about £10 to £15 to the cost of the helmet and that is driving up the price of many helmets, however most manufacturers will argue that the extra cost is justified by the safety improvement.
Bontrager have produced a nice video which shows the MIPS technology in action.