vy.p334659wrote a review of Sea To Summit X-Mug Collapsible Mug on July 29, 2015
Familiarity: I've used it several times
Taking off 1 star from an otherwise incomparable collapsing mug. Silicon will always hold onto oils and is very difficult to get clean in the backcountry. I discovered this somewhere in the Cascades, with a cup of Willamette pinot smelling powerfully of bacon, coffeee and Dr. Bronner's Lavender Magic Soap. This cup had been thoroughly cleaned - the essential oils from the soap and other foods had attached to the silicon. The smell only went away when boiling the cup in clean water an oily white residue collected on top of the water.
Lesson learned: don't use scented magic soap.