Thermos Mountain FFX Flask 900 ml

The Thermos Mountain FFX 900 ml is the largest model in the range, aimed more at multi-day trips or sharing a drink within a group than solo daytime sipping. Its 36-hour heat and 40-hour cold retention rate among the strongest in this flask category — the manufacturer also states liquid stays above 77°C after 6 hours, a more concrete figure than a generic "keeps it hot" claim. A loop on the cap lets you clip the flask to a carabiner outside the pack, and replacement parts are available, extending the flask's usable life instead of retiring the whole unit when a seal wears out. A silicone grip ring protects the body when set down on rock and improves grip with wet hands. At 390 g it is the heaviest in the FFX line, and combined with the 900 ml capacity it clearly sits outside ultralight territory — this is a pick for mountain trips where having a generous supply of hot drink all day matters more than shaving weight. The steel is BPA-free, the seal is leak-resistant, and it is not dishwasher safe.