This is different from the Warm Coat mod. It does not reduce the effect of the Ice environmental hazard, which is a reduction to max shields, but instead damage of the type Cold.
As with all resistance mods, the resistance value is subtracted from the respective damage type's modifier against the user's health type and shield type. This reduces the shield modifier from 1.5 to 0.9 and the health modifier from 1 to 0.4. It thereby increases effective shields against Cold by ~+66.7% and effective health against Cold by +150%.