Question: My brown (cloth) scapular breaks frequently. Is it “OK” to wear a medal scapular?
Do I need to have each (new) scapular blessed?
Yes, but some restrictions apply here. The scapular is generally blessed at an investiture ceremony, in other words, those who wear the scapular shouldn’t just initially buy it in a store and start wearing it. They should have some affiliation with a religious order that uses it as part of their habit. For example, I was a parishioner in Our Lady of Mount Carmel parish when I was a child and we would often pray to Our Lady of Mt. Carmel on her feast day and then all would be given a scapular which would be blessed in a ceremony.
If that scapular (which is usually made of two pieces of wool held together by cloth laces) breaks, you can simply buy a new one–and that needs not to be blessed again. The former blessing transfers to the new object in this instance from the investiture ceremony.
As far as a metal scapular goes, they are fine to wear. One side should have a picture of the Sacred Heart on one side and Mary, the Mother of God on the other. You must first have already been invested with a blessed woolen scapular first and then have the medal blessed to replace the woolen scapular.
The important thing to note here is the desire to wear one constantly if one desires to gain the indulgences and privileges of the sacramental.