While researching the HI distribution around the Supernova remnants we have found 4 broad (diameter 70-300 ps) and hence old (age 2-9 mln. years) HI envelopes around the Supernova remnants having, characteristics of plerions, i.e. obviously young objects with ages of the 1000 - 10000 years. The example of one such object is adduced on figure 1. It is clear, that the shock wave of the remnant could not result in motion this gas and the calculation of envelopes parameters was carried out in the supposition, that acted stellar wind of the presupernovae star.
It has allowed to estimate mass of stars and also mass of gas dropped at explosion.The kinematics ages of envelopes do not exceed life time of these stars on main sequence. Besides,the found objects testify that, at least in some cases the evolution of the remnant happens in matter with very low density, that is rather important for an evaluation of the characteristics of the Supernovae remnant.

Figure 1. The distribution of details of the HI line emission around the Supernovae 3C 396 remnant. The strokes show a clumped HI envelope.