A sealing device for sealing a cover material with fluctuating thickness onto sealing regions of a blister web or of at least one blister cap, wherein the sealing regions of the blister web or of the at least one blister cap surround at least one pocket for receiving a product, the sealing device comprising: a first, heated sealing tool; a second sealing tool which comprises at least one recess for receiving at least one pocket of the blister web or of the at least one blister cap, wherein the first sealing tool and the second sealing tool are arranged opposite to one another; a first intermediate element composed of an elastic material, wherein the first intermediate element is composed of a silicone elastomer and is attached to the first sealing tool on the side facing the second sealing tool; and a second intermediate element composed of a thermally insulating or poorly thermally conductive material which is different from the material of the first intermediate element; wherein the first sealing tool with the first intermediate element and the second sealing tool with the second intermediate element are movable relative to one another between an open position, in which they are spaced apart from one another to accomodate the blister web or the at least one blister cap and at least one portion of the cover material, and a closed sealing position, in which at least portions of the first intermediate element and of the second intermediate element exert pressure on one another, characterized in that the first intermediate element has a thickness of 0.3 mm to 2 mm, the second intermediate element has a thickness of 5 mm to 15 mm and is attached directly to the second sealing tool on the side facing the first sealing tool, and the first sealing tool and the second sealing tool are configured in such a way that, in the closed sealing position, the first intermediate element bears against the cover material and the second intermediate element bears against the webs of the blister web or of the blister cap. a first, heated sealing tool; a second sealing tool which comprises at least one recess for receiving at least one pocket of the blister web or of the at least one blister cap, wherein the first sealing tool and the second sealing tool are arranged opposite to one another; a first intermediate element composed of an elastic material, wherein the first intermediate element is composed of a silicone elastomer and is attached to the first sealing tool on the side facing the second sealing tool; and a second intermediate element composed of a thermally insulating or poorly thermally conductive material which is different from the material of the first intermediate element; wherein the first sealing tool with the first intermediate element and the second sealing tool with the second intermediate element are movable relative to one another between an open position, in which they are spaced apart from one another to accomodate the blister web or the at least one blister cap and at least one portion of the cover material, and a closed sealing position, in which at least portions of the first intermediate element and of the second intermediate element exert pressure on one another, characterized in that the first intermediate element has a thickness of 0.3 mm to 2 mm, the second intermediate element has a thickness of 5 mm to 15 mm and is attached directly to the second sealing tool on the side facing the first sealing tool, and the first sealing tool and the second sealing tool are configured in such a way that, in the closed sealing position, the first intermediate element bears against the cover material and the second intermediate element bears against the webs of the blister web or of the blister cap.