Premier Flex is extremely durable and made from .015 Stainless Steel. It features an interlocked design to maximize strength and flexibility. It’s the most rugged liner we recommend for those tight winch-able situations. Premier Flex 316 can be used for all fuel burning appliances including; wood, wood pellet, oil, gas, and corn. Premier Flex 304 can be used for wood burning appliances. Premier Flex can withstand being ovalized and rectanglized to accommodate for unusual offsets or rectangular chimneys. When a liner is taken “out of round” it does reduce the cross sectional area.