Described herein are flexible seals for directing fluid flow in a tubular reactor, such as a reformer, for enhancing heat transfer and reactor efficiency. The seals can be made of corrugated metal foil that is expandable in the radial direction for accommodating the expansion and contraction of reactor components in the tubular reactor during operation. The seals can block or redirect fluid flow through the reactor. Fluid is directed to the interior of the reactor by the seals and bypass around the outer circumference of the reactor components is reduced or eliminated.