Abstract: Seal ring made of an elastomeric material intended to operate at a temperature at least equal to 150.degree. C and to be in contact on its opposite sides with two mediums one of which at least is a medium emitting nuclear radiations and to be able to slide with a very slight friction coefficient in contact with a body which rotates and/or moves in a linear direction, comprising a body with an outer casing made of an elastomer which is resistant to heat and to nuclear radiations and has a low friction coefficient and with an inner casing made of a heat resisting elastomer, the outer and inner casings being closely welded to each other, the body being filled with a low-pressure gas and the inner casing being impermeable to the gas for filling the body. Application to seal rings for vessels in a radioactive medium.