A size adaptive protective headgear comprising - a protective shell comprising, - a first and a second front cut (112, 114) extending respectively from a first and second side edge of the protective shell, the first and second front cut (112, 114) enabling expansion and contraction of a front section of the protective shell, and - a first and a second rear cut (138, 140) extending respectively from a first and second side edge of the protective shell, the first and second rear cut (138, 140) enabling expansion and contraction of a rear section of the protective shell, the first and second front cut (112, 114) extend in a first direction (120, 122) towards the opposite side of the protective shell, and in a second direction (124, 126) towards the rear end of the shell, characterized in that, the first and second front cut (112, 114) extend in a third direction (134, 136) towards the rear end of the protective shell, the third direction (134, 136) diverging from the second direction (124, 126) towards the same first and second side edge (116, 118) where the first and second front cut (112, 114) extends from, the first and second rear cut (138, 140) extend in a first direction (142, 144) towards the opposite side of the protective shell, and in a second direction (124, 126) towards the front end of the protective shell, the first and second rear cut (138, 140) extend in a third direction (152, 154) towards the front end of the protective shell, the third direction (152, 154) diverging from the second direction (124, 126) towards the same first and second side edge (116, 118) where the first and second rear cut (138, 140) extends from, and wherein said first and second front cuts (112, 114) are essentially symmetrical with the first and second rear cuts (138, 140) so that the rear cuts (138, 140) are mirrored to the front cuts (112, 114). - a protective shell comprising, - a first and a second front cut (112, 114) extending respectively from a first and second side edge of the protective shell, the first and second front cut (112, 114) enabling expansion and contraction of a front section of the protective shell, and - a first and a second rear cut (138, 140) extending respectively from a first and second side edge of the protective shell, the first and second rear cut (138, 140) enabling expansion and contraction of a rear section of the protective shell, the first and second front cut (112, 114) extend in a first direction (120, 122) towards the opposite side of the protective shell, and in a second direction (124, 126) towards the rear end of the shell, characterized in that, the first and second front cut (112, 114) extend in a third direction (134, 136) towards the rear end of the protective shell, the third direction (134, 136) diverging from the second direction (124, 126) towards the same first and second side edge (116, 118) where the first and second front cut (112, 114) extends from, the first and second rear cut (138, 140) extend in a first direction (142, 144) towards the opposite side of the protective shell, and in a second direction (124, 126) towards the front end of the protective shell, the first and second rear cut (138, 140) extend in a third direction (152, 154) towards the front end of the protective shell, the third direction (152, 154) diverging from the second direction (124, 126) towards the same first and second side edge (116, 118) where the first and second rear cut (138, 140) extends from, and wherein said first and second front cuts (112, 114) are essentially symmetrical with the first and second rear cuts (138, 140) so that the rear cuts (138, 140) are mirrored to the front cuts (112, 114). - a first and a second front cut (112, 114) extending respectively from a first and second side edge of the protective shell, the first and second front cut (112, 114) enabling expansion and contraction of a front section of the protective shell, and - a first and a second rear cut (138, 140) extending respectively from a first and second side edge of the protective shell, the first and second rear cut (138, 140) enabling expansion and contraction of a rear section of the protective shell, the first and second front cut (112, 114) extend in a first direction (120, 122) towards the opposite side of the protective shell, and in a second direction (124, 126) towards the rear end of the shell, characterized in that, the first and second front cut (112, 114) extend in a third direction (134, 136) towards the rear end of the protective shell, the third direction (134, 136) diverging from the second direction (124, 126) towards the same first and second side edge (116, 118) where the first and second front cut (112, 114) extends from, the first and second rear cut (138, 140) extend in a first direction (142, 144) towards the opposite side of the protective shell, and in a second direction (124, 126) towards the front end of the protective shell, the first and second rear cut (138, 140) extend in a third direction (152, 154) towards the front end of the protective shell, the third direction (152, 154) diverging from the second direction (124, 126) towards the same first and second side edge (116, 118) where the first and second rear cut (138, 140) extends from, and wherein said first and second front cuts (112, 114) are essentially symmetrical with the first and second rear cuts (138, 140) so that the rear cuts (138, 140) are mirrored to the front cuts (112, 114).