aforenoted parent application ser no 573 953 this latter feature permits a wider variation in the disposition of the panel while assuring efficient uninterrupted fluid flow further notable features of the panel of fig1 comprise the configuration of headers 20 39 and the placement of inlet 21 39 and outlet 22 39 at the respective widest portions of the headers also bonded portions 26 present in headers 20 39 are aligned so as to assist in the uniform distribution of fluid flow therethrough the particular advantages of this panel design will be more fully developed in our copending application ser no 632 643 the disclosure of which is incorporated herein by reference in this illustration panel 19 39 is of course provided with a nib like marker structure 24 39 centrally located in association with a connecting portion 23 39 in addition to the placement of a nib like distension in direct association with an inflated portion of the panels prepared in accordance with the present invention the marker structure of the present invention may comprise a bonded portion located within an expanse of unbonded area referring particularly to fig1 a solar collector panel 27 is depicted which comprises a unitary expanse of unbonded area wherein continuity exists between the header area and the area comprising the connector portions thus unitary collector area 28 is broken up only by a symmetrical pattern of bonded portions bonded portions 29 effectively break up fluid flow and permit the efficient.