In this work we have shown that the free, apo and holo forms of the sensing domain of the fluoride riboswitch from T. petrophila could be reproducibly formed in vitro. However, a significant population of unfolded or disordered aptamer was present in all PELDOR samples manifesting as distance distributions tailing up to 50 Å and beyond. Nevertheless, PELDOR has revealed a preorganisation similar to the B. cereus fluoride riboswitch with the exception that also F -was required for pseudoknot formation. Modelling the widths of distance populations based on the single backbone conformation of the crystal structure matched the experimental distributions for F ENDOR but significantly underestimated the experimental PELDOR distance distributions. Thus, the combined PELDOR and F ENDOR results indicated a preorganised riboswitch structure with a more rigid F --binding site and more conformations sampled at the periphery.