The Q-region of Kππ mass (i.e. 1.10 ⩽ M(K ππ) < 1.5 GeV) is studied for the reactions K +p → K +π+π-p (≈ 77 000 events) and K +p → K seen0π+π0p (≈ 19 000 events). The data samples correspond to K +p interactions at fourteen beam momenta in the range 2.5 - 12.7 GeV/ c. The production and the decay of the of the K ππ system are analysed as a function of the incident energy and the K ππ mass. It is shown that the differential cross section d σ/d tpp shrinks when the incident energy increases. The spin-parity is found to be predominantly 1 + for the whole Q-region and the density-matrix elements do not vary with the energy or the K ππ mass. The ratio of the number of Kϱ to the number of K∗π events is obtained from a fit of the decay Dalitz plot and found to be maximum for 1.25 ⩽ M (K ππ) < 1.30 GeV.