In the current cosmological scenario, part of the linearly polarized emission of the CMB is expected to be rotational (B-modes). This component is due to tensor perturbations of the metric produced by primordial gravitational waves, which are generated a split-second after the Big Bang. The signal expected is of the order of ≳0.1 μK, well below the non-rotational component of the polarization signal (E-modes), and beyond the sensitivity of present generation instruments. New, more sensitive instruments are developed in several labs, with the goal to measure the B-modes. Control of systematics and foregrounds will be the key to make the results of these experiments believable. In this paper we shortly outline BRAIN, a bolometric interferometer devoted to B-modes research, and its pathfinder experiment, devoted to test the Dome-C site.