It all depends on the size... Folding flat Kevlar bead tires make great 3rd tires.
for spares, But a 27" /700c tire can be shall we say Bandsaw blade like reduced in diameter
for travel as well it rolls up in 3rds, by forming ins figure 8 and then into 3 rings.

light skin wall not HD tires .. Kevlar bead or there is A Kevlar puncture protective band
to reduce puncture vulnerability.

have specific tires in mind?