This study was undertaken to develop a linear expansion method for identifying transition temperatures in elastomers that would be experimentally easier than dilatometry. It was considered desirable to use isotropic elastomer samples. Anisotropic as well as isotropic samples were unavoidably prepared; this led to interesting-results. Filler type, compounding, and molding procedures were each important factors in contributing to anisotropy of elastomers. The elastomers included in this study were natural rubber, butyl rubber, and a series of polysiloxane polymers. Orientation within an elastomer leads to: (a) Greater linear thermal expansion and swelling in the direction perpendicular to orientation, (b) More than one Tg value for some, but not all, elastomers. (c) Increases in ΔTg ranging up to 11° C for the siloxane copolymer elastomers, 15° C for the butyl rubber and 3° C for natural rubber. Isotropic elastomers have equal coefficients of expansion in all directions and one Tg value. An explanation for the shift in Tg is given, assuming a directionally dependent amplitude of vibration concept and that Tg is proportional to inter-molecular binding forces.