an article of manufacture that has at least three layers of heat sealable material . there is at least one first heat seal between at least two of the layers in a first area effected at a first temperature . there is also at least one second heat seal between at least two more layers , where at least one of these two layers is distinct from the at least two layers joined by the first heat seal , in a second area effected at a second temperature , where the second temperature is different than the first temperature , thereby allowing for heat sealing of discrete areas of the article in discrete steps .