In the mechanized packing processes some problem makes the strength of the freshly formed still a not completely solidified heat seal what in a particularly drastic way shows itself in the vertical form, fill and seal system where in the filling of the package the product falling from the feed hopper impacts the freshly formed seal. The fundamental significance for the assessment has in this case the measurement of the property called hot tackto after its English name, i.e., of the strength showed by the heat seal directly after sealing. The apparatus SL-10 HT/ST used in the Polish Packaging R.&D.Centre for testing hot tack both in the polyolefine films and laminates with the share of sealing layers is characterised. The model results of measurements confirming the significance of hot tack for the correct assessment of the tested laminate usefulness in processing conditions are discussed.