Bernhard Kuemel wrote:
So ... what would be the best material to fill the gap between 2
concentric glass tubes? Polyester, Epoxide, PU, Polycarbonate,
Polyvinylbutyral, ...? It should be managable with low tech equipment.

Actually I first thought of filling the gap with a viscous liquid like
glycerol or silicone oil.

A test explosion of a 1 cm OD pressure tube shattered a 60mm OD
borosilicate glass tube with 7mm wall to rather large pieces. I think,
if the outer tube were not struck by the glass fragments of the pressure
tube, the protective glass tube will withstand the shock wave. The
pressure in the pressure tube (10mm OD, 5.5mm ID) may exceed 200bar. It
was up to 240 bar without breaking.

With a laminated glass tube, is there a possibility that the glass will
crack from thermal expansion of the resin layer? The resin also should
not separate from the glass as this would create additional optical
surfaces which decrease optical transparency.

Bernhard