Thermal conductivity measurement of an individual millimeter-long expanded graphite ribbon using a variable-length T-type method

•A new expanded graphite ribbon (EGR) is obtained by compressing a single piece of expanded graphite.•The EGR has a micrometer-sized thickness and a millimeter-sized length.•The thermal conductivity of EGR is measured accurately using a variable-length T-type method.•The longitudinal thermal conductivity reaches up to 335.6±27.4 W m−1 K−1 at 300 K.•The thermal conductivity keeps decreasing with temperature rising from 300 K to 380 K.