Rab altus vest ebony the altus vest is a new lightweight cirrustm synthetic insulated vest designed for use in cold damp and changeable environments cirrustm synthetic insulation combines the warmth and weight benefits of down with the wet weather performance of synthetics designed primarily for use in changeable unknown conditions the altus can be worn as an outer or mid layer the slim fit and elasticated armholes lend it to technical climbing and the ultra lightweight and durable perte