Are potatoes ,carrots and sweet potato included ?
All fruit and vegetables are high in fiber including potatoes, carrots and sweet potatoes.
Don't wrap with aluminum foil.it is a fairly good heat conductor (and you want a heat insulator)Felt material is a fairly good insulatorAn expanded plastic (such as polystyrene foam) is a good insulatorMany layers of newspaper (loosely wraped around the glass container make a fairly good, readily available, insulator.
the best insulator would be vacuumprobably impracticle to achievenewspaper has long been used as insulationstyrofoam would be good.
First wrap it in newspapers with polystyrene on top of thatFinally, wrap 2 sheets of Aluminium foil around the styrene.One sheet with shiny side ouside and the other with shiny side insideThe same will work to keep something cool.
Plastic is a fair insulator, but only Aluminum is worse on your listCotton should work well, but it has to be dryA wool sweater or sawdust should work betterKeep in mind that thickness is important tooFelt is a good insulator.
