This Journal is planning to publish the review series on the NMR in the analysis of soft materials. This review is the introduction to the series. The advantage of NMR is, at first, introduced from the relationship with polymeric materials; namely, mobile solid materials. The adjective on mobility is ambiguous in Japanese language, in which there are no different terms corresponding to soft and flexible. In order to avoid this ambiguity during the research on soft materials, an example is introduced in the past silk industry. Soft but pliable silk fabrics have been appreciated in the industry. The concept of relaxation times is different in rheology and NMR. This difference is explained and the relationships between both relaxation times. Finally, NMR relaxation times are applied to the estimation of physical properties of historically aged silk materials from 10^th to 18^th centuries with the aid of the fluctuation-dissipation theorem developed by Einstein. NMR is free from the stress-centralization during the measurement. This advantage is used the final application. Loss tangents are almost identical between historical and fresh silks, and standard deviations of the loss tangents decrease from old to recent years.