The type of triangle that will always have exactly 1 fold reflectional symmetry is the isosceles triangle.
An isosceles triangle has two sides of equal length and one side that is of a different length. The line of symmetry in an isosceles triangle runs down the middle, from the vertex angle (the angle between the two equal sides) to the base (the unequal side). This line divides the triangle into two mirror-image halves, thereby creating exactly one fold of reflectional symmetry.
In contrast, an equilateral triangle has three lines of symmetry, and a scalene triangle has none. Therefore, the isosceles triangle is the only type that consistently features a single line of reflectional symmetry.