On paper, most of the test kits are from iHealth Labs, but they are a US subsidiary of Andon Health, a Chinese company, who actually manufacture the test kits (
https://news.yahoo.com/chinas-andon-health-supply-home-005352302.html ). From their webpage about the test kits,
https://ihealthlabs.com/ :
The manufacturer of the iHealth® COVID-19 Antigen Rapid Test requires test kits be stored at temperatures between 36o and 86oF (2o - 30oC). Any extended exposure of the test kit to temperatures beyond this range may affect quality of test results.
