Abstract: An insulation device having: a tubular and pliable joint member, the joint member comprising a first end region and a second end region opposite to the first end region, the second end region being fastened to the first end region at a junction area so as to form a joint loop, and a flexible sleeve comprising a tubular central portion, a first end portion and a second end portion disposed on either side of the tubular central portion, the first end portion being folded toward the interior of the tubular central portion, the second end portion being folded toward the interior of the tubular central portion, the flexible sleeve being mounted about the joint loop and configured to cover the junction area. The present invention also concerns a folding tool and a method for folding and mounting the insulation device.