A thermoplastic mounting medium (25) configured for embedding and subsequently fixating a sample material (10) in a moulding cavity (11) by means of sintering or melting the thermoplastic mounting medium (25) to become a monolithic bulk material at least partially accommodating said sample material (10) The thermoplastic mounting medium (25) includes a mixture of: polymer mixed with organic fibres, and thermally conductive filler having a thermal conductivity of minimum 5 W/(m×K) wherein the thermally conductive filler is mixed homogeneously with the composite material and wherein that the thermally conductive filler represents at least 30% w. of the thermoplastic mounting medium.