Hatmana

From Halachipedia
  1. Many permit putting hot water into a thermos, while others forbid as a problem of hatmanah on Shabbat. [1]

References

  1. Chazon Ish 37:35, Az Nidbaru 1:48-9, 3:17, Igrot Moshe 1:95, oral ruling from Rav Elyashiv (quoted by Shalmei Yehuda 6:4) are lenient against the Sh”t Shevet HaLevi 1:93 who is stringent in this regard.