Great question on the Butterfly differences.
Back in the day pads only had protection on the front, in the 80's new "flaps" were added to the inside of the pad allowing the goaltenders added protection to the inside of there legs. These flaps started out super thin to protect goalies who would make saves by turning there legs out to the now super thick inside padding that allows the goalies to go down on them, now it allows goalies to go down into the butterfly while leaving the pads level to the ice.
