H-1 Magic Angle Spinning (MAS) NMR and H-1 T-1 and T-1rho relaxation times measurements were used to investigate structural aspects of gel derived glasses of composition 10P(2)O(5).90SiO(2) (10P) and 30P(2)O(5).70SiO(2) (30P), with the aim of understanding the different humidity sensitive behaviour observed for films of the same composition. The experimental evidence suggests that 10P and 30P gel samples heat treated at 100 degreesC have a similar POH environment while further heating causes a different structural evolution of POH units. In particular, the 30P sample heat treated at 400 degreesC shows a single H-1 resonance while a number of resonances are seen in the H-1 spectrum of the 10P sample heat treated at 400 degreesC. Further evidence of the different structure of 10P and 30P samples was given by the NMR relaxation times measurements, the gels were found to be heterogeneous on a nanometric scale. Domains, about 60 nm in size, related to H-1 resonance in POH were evenly distributed in the matrix of both gels, only in the 10P gel also larger domains (about 700 nm) were found that can be related to H-1 resonance in SiOH groups. Finally, MAS in combination with variable temperature static NMR spectra provided detailed information on the network structural features present in the 30P sample heat treated at 300 degreesC as well as in the 10P sample heat treated at 400 degreesC and allowed investigation of the dynamic processes taking place in these samples.