Give it basalt composite fibers.

Foam and highly insulative basalt composite fibers (possibly a layer or
two of basalt micro-balloons to boot) is just the ticket to ride, and I
believe it's well proven as well as being dirt cheap at perhaps
representing less overall mass per R-factor. In fact, the entire tank
could have been a 100% composite of basalt and perhaps a touch of
silica if need be.
~

Don't look: in spite of the orchestrated status quo, it seems there's
been other life upon Venus
http://guthvenus.tripod.com/gv-town.htm
Russian/China LSE-CM/ISS (Lunar Space Elevator) as situated within the
ME-L1/EM-L2 sweet-spot
http://guthvenus.tripod.com/lunar-space-elevator.htm
Venus ETs, Earthly ETs plus a few other somewhat testy topics by; Brad
Guth / GASA-IEIS
http://guthvenus.tripod.com/gv-topics.htm