Thermal conduction in a tangled magnetic field

The suppression of thermal conduction by a static stochastic magnetic field is calculated for different ratios of the field scale length to the collisional mean free path. The effects of magnetic trapping an determined through a two-scale analysis acid Monte Carlo particle simulations. In galaxy-cluster cooling flows, thermal conductivity is reduced from the Spitzer value by a factor of order 10(2) to 10(3).