In the current cosmological scenario, part of the linearly polarizedemission of the CMB is expected to be rotational (B-modes). Thiscomponent is due to tensor perturbations of the metric produced byprimordial gravitational waves, which are generated a split-second after theBig Bang. The signal expected is of the order of ≲ 0.1 μK, well below the non-rotational component of the polarizationsignal (E-modes), and beyond the sensitivity of present generationinstruments. New, more sensitive instruments are developed inseveral labs, with the goal to measure the B-modes. Control ofsystematics and foregrounds will be the key to make the results ofthese experiments believable. In this paper we shortly outlineBRAIN, a bolometric interferometer devoted to B-modes research,and its pathfinder experiment, devoted to test the Dome-C site.