1. A RAILWAY TANK CAR COMPRISING AN ELONGATED LONGITUDINALLY EXTENDING TUBULAR BODY DISPOSED IN A SUBSTANTIALLY HORIZONTAL POSITION, AND BODY INCLUDING AN OUTER SHELL OF STRONG RIGID SELF-SUPPORTING METAL STRUCTURE, A PAIR OF LONGITUDINALLY EXTENDING AND ALIGNED STUB DRAFT SILLS EACH OF STRONG RIDIG METAL STRUCTURE AND RESPECTIVELY DISPOSED BELOW THE OPPOSITE ENDS OF SAID OUTER SHELL AND RIDIGLY SECURED THERETO, WHEREBY DRAFT AND BUFF FORCES ARE APPLIED BETWEEN SAID STUB DRAFT SILLS THROUGH SAID OUTER SHELL, A PAIR OF LONGITUDIANLLY SPACED-APART AND LATERALLY EXTENDING BODY BOLSTERS RESPECTIVELY CARRIED BY SAID SUBDRAFTS SILLS, A PAIR OF WHEELED TRUCKS RESPECTIVELY DISPOSED BELOW AND IN SUPPORTING RELATION WITH SAID BODY BOLSTERS, SAID BODY ALSO INCLUDING AN INTERMEDIATE LAYER OF RESILIENT CELLULAR MATERIAL COMPLETELY ENCLOSED BY SAID OUTER SHELL, SAID BODY FURTHER INCLUDING AN INNER LINER OF FLUID-TIGHT CONSTRUCTION COMPLETELY ENCLOSED BY SAID INTERMEDIATE LAYER, THE OUTER AND INNER SURFACES OF SAID INTERMEDIATE LAYER BEING RESPECTIVELY INTIMATELY BONDED TO THE INNER SURFACE OF SAID OUTER SHELL AND TO THE OUTER SURFACE OF SAID INNER LINER, SAID INTERMEDIATE LAYER HAVING A SUBSTANTIAL THICKNESS IN ORDER COMPLETELY TO SEPARATE AND TO ISOLATE SAID OUTER SHELL FROM SAID INNER LINER AND RESILIENTLY TO SUPPORT SAID INNER LINER UPON SAID OUTER SHELL, SAID INTERMEDIATE LAYER CONSISTING ESSENTIALLY OF A BLOWN POLYESTER-URETHANE RESIN OF CLOSED-CELL STRUCTURE ENTRAPPING SUBSTANTIAL INERT GAS, WHEREIN SAID INERT GAS CONSISTS ESSENTIALLY OF A CHLORINE-FLUORINE SUBSTITUTED ALKANE, WHEREBY SAID INTERMEDIATE LAYER HAS A K FACTOR AT LEAST AS LOW AS ABOUT 0.15 B.T.U/IN. SQ. FT./HR./*F. IN ORDER TO HEAT-INSULATE FROM EACH OTHER SAID OUTER SHELL AND SAID INNER LINER, AND WHEREBY SAID INNER LINER MAY SAFETY CARRY LADINGS HAVING TEMPERATURES IN THE RANGE -50*F. TO +300*F. WITHOUT DAMAGE TO SAID INTERMEDIATE LAYER, A TUBULAR FITTING CARRIED BY SAID BODY, THE INNER END OF SAID FITTING BEING SEALED IN FLUID-TIGHT RELATION WITH AN OPENING PROVIDED IN SAID INNER LINER AND THE INTERMEDIATE PORTION OF SAID FITTING PROJECTING THROUGH A PAIR OF ALIGNED HOLES RESPECTIVELY PROVIDED IN SAID INTERMEDIATE LAYER AND IN SAID OUTER SHELL AND THE OUTER END OF SAID FITTING BEING ACCESSIBLE FROM THE EXTERIOR OF SAID OUTER SHELL, THEREBY TO ACCOMMODATE THE PASSAGE OF A FLUID LADING THROUGH SAID FITTING BETWEEN THE INTERIOR OF SAID INNER LINER AND THE EXTERIOR, MEANS CARRIED BY SAID FITTING FOR SELECTIVELY OPENING AND CLOSING THE PASSAGE THERETHROUGH, AND A BODY OF HEATINSULATING MATERIAL ARRANGED IN SURROUNDING RELATION WITH THE INNER END AND THE INTERMEDIATE PORTION OF SAID FITTING AND WITHIN SAID HOLES IN ORDER TO MINIMIZE HEAT-TRANSFER ALONG SAID FITTING BETWEEN SAID OUTER SHELL AND SAID INNER LINER.