Stanley 2-Liter Thermos Only Keeps Water Hot for 8 Hours

A 2-liter Stanley thermos I purchased on Amazon in 2026 is falling far short of my expectations when it comes to heat retention. Even when I fill it with boiling water, it starts to cool down noticeably after just 8 hours. From a brand like Stanley, especially in a thermos this size, I would expect at least 48 hours of heat retention — so this level of performance is a real disappointment.
I believe this may be a manufacturing defect and am asking that the thermos be inspected and, if possible, replaced or refunded at full value. I would appreciate a prompt review of my issue and a timely response.