[Mondial]

I certainly does look like asbestos. It was pretty common in the 30's and 40's to use asbestos fiber sheet under the chassis and in the cabinet near power tubes. I have a Philco 40-120 with the same type of asbestos in the wooden cabinet under the chassis. The earliest Zenith Transoceanics also had asbestos under the chassis.

If it were my radio, I would try not to disturb it to minimize getting any fibers airborne. When working around it, wear a respirator approved for asbestos and do it over a disposable surface. It is usually recommended to thoroughly wet down the asbestos with water so it will not become airborne when disturbed.