Materials: Flame resistance: Must be 100% IFR and NFP701 Compliant via Immersion method....
then
Curtain Fabric: Must be 100% Cotton IFR
Products: KM Fabrics "Memorable" 25oz Velour.
Wait, we're really drifting from the fullness question.
Ok, for those that don't read specs all day long.
"IFR" is Inherently Flame retardant and typically used to refer to Polyester fabrics for Draperies.
"Immersion Method" is the process used to flame treat cotton fabrics. Cotton is NOT IFR.
KM Fabrics "Memorable" is a Cotton Velour.
All of this results in writing a Request for information before you even get started on a project.
here in W Australia we don't have your problem as virtually all stagedrapes are wool and are as fireproof as sheep, unfortunately most are specified with fullness, which is amateurish in my opinion, blacks are supposed to disappear, not be a feature.