From the Advancement and Merit Badge Handbook by the BSP
The Merit Badge Sash is made of the same material as the pants of your uniform. It is worn over the right shoulder, cutting diagonally across the chest with the other edge touching the left hip bone.
The sash may be bought from your local Scout Shop. The badges earned are sewn on the sash in two rows one-fourt inche (1/4") apart from each other.
The first two (2) badges should be sewn in a way that when the sash is worn, they are just at the intersection of an imaginary line that runs along the middle of the sash and the one that runs vertically along the middle of the sash and the one that runs vertically along the middle of your shirt. The succeeding badges are sewn alternately starting above then below the first two (2) badges. The bottom portion of the badges should be perpendicular to the edges of the sash.
The Merit Badge sash should be worn only during the following occasions:
1. When attending Courts of Honor/Recognition and/or other ceremonical functions.
2. When visiting Jamborees, Youth Forums and other Scouting activities of at least municipal/district level.
3. When appearing before a Board of Review.
4. During such occasions as may be prescribed by appropriate authority.
Source: Merit Badge Center Philippines