SHAFAQNA – The Grand Ayatollah Makarem answered a question about sewn Ihram garb.
Question: Is sewn clothing which is Haram for men in Ihram condition, the same as sewn pieces which are joined together, or there is a problem even with stitches on towels for Ihram?
The Grand Ayatollah Makarem: There is no problem with these sewing. And the clothing which are Haram for men who are in Ihram condition include: clothing like shirt, jacket/coat, trousers, underwear, short.
Source: PERSIAN SHAFAQNA