This paper presents an analysis of the transient thermal performance of dynamic insulation. A modelbased on heat transfer through porous media is introduced, considering two types of boundaryconditions: (1) indoor temperature and outdoor temperature are constant; (2) indoor temperature isconstant while outdoor temperature changes. By solving the model numerically, it is found that for thefirst kind of boundary condition, the temperature profile in the wall will reach steady-state within onehour, when the porosity is high. It will take a longer time for this purpose if the porosity decreases. Forthe second kind of boundary condition, the results illustrate that the interior surface temperature of thedynamic insulation swings with the change of the environment temperature. Influenced by thetransient effect, the interior surface temperature of the dynamic insulation is different with that underthe steady-state. However, by comparing the heat loss obtained under the transient and steady-statecondition, it is noticed that the difference is not significant. This means that heat transfer coefficientsderived from steady-state analysis, such as dynamic U-value, are good approximations concerning theenergy consumption of buildings with dynamic insulation, and are convenient tools for engineeringimplementation.