Sealing device with increased surface roughness

A sealing device comprising a functional layer having a first major surface and a second major surface and a barrier layer directly or indirectly connected to the second major surface of the functional layer, the functional layer comprising:

• a) 20-75 wt.-%, of at least one thermoplastic polymer, and
• b) 25-80 wt.-%, of at least one solid filler,
• all proportions being based on the total weight of the functional layer, wherein
• the first major surface of the functional layer has a surface roughness having a waviness factor, determined as the product of the root mean square roughness of waviness and peak density of waviness, of at least 0.0125 1/mm, wherein the waviness factor and the peak density waviness are determined according to ISO 25178 standard from a waviness profile obtained from a measured primary profile using a cutoff length of 0.8 mm.