<p>A heat trap (70, 150) for use in a conduit (28) through which fluid flows. The heat trap comprises a unitary body having a central bore (113) extending therethrough, and first and second blocking portions (125) having on a circumferential edge respective first and second resilient hinge portions (130). Both of the blocking portions substantially entirely block the central bore when in an at-rest condition. The first and second hinge portions hingedly interconnect the blocking portions to the unitary body in cantilever fashion and permit resilient deflection of the blocking portions on the hinge portions in response to fluid flow through the conduit. The resilient hinges also provide for the resilient return of the blocking portions to the at-rest condition in the absence of fluid flow through the conduit. The unitary body and the first and second blocking portions define therebetween a substantially stagnant zone (140) to resist convective heat transfer from fluid on one side of the stagnant zone to fluid on the other side of the stagnant zone.</p>