Shalom. There is a type of undershirt available on the market made of partially synthetic material with Tzitzit attached (http://www.mishkan-hatchelet.co.il/חולצתגופיית-ספורט/1187-חולצת-ספורט-מידה-s.html). This undershirt has snap-ons to connect. Is it permissible to wear this undershirt outside on Shabbos/Yom Kippur (provided that the Tzitzit are intact)? Are the snap-ons allowed to be snapped together on Shabbos/Yom Tov? Thank You.
I apologize for the delay in answering this question.
There is no problem in wearing this undershirt on Shabbos, since “carrying” tzitzis is not considered “carrying” (but rather “wearing”), and the fact that they snap on does not make a difference.
It is also permitted to snap them on, since the “snap-on” is made to open and shut, and is permitted for use on Shabbos just as buttons are.