Sea to Summit Passage Insulated Mug

A solid, plus-sized, insulated mug, nestable to minimize space in the pack. Graduated markings on inside are hard to read, and the lid is not completely spill-proof.

I am on a quest for the backpacker’s grail: a mug that is 1.lightweight, 2. voluminous, 3. well-insulated, 4. spill-proof, 5. easy to wash, 6. takes up little room in the pack, and 7. will pack up the tent while I eat my breakfast. Actually, two mugs, since my wife and I usually hike together, and that doubling-up is the reason we decided to spring for the Sea to Summit (herein: S2S) Passage Mug—my fourth try for the grail.

After going through a series of early contenders, most of which lacked two or more of the properties listed above (none of the entries so far will do #7), the real quest began over 10 years ago with one of the Passage’s predecessors, the long-discontinued S2S Delta Insul-mug.

Then about 8 years ago I found the GSI Outdoors Infinity Insulated mug lurking in a dark corner of an outfitter's store in Colorado. It won easily in a head-to-head competition (see my review) with the Delta and became our mug of choice for 7 or 8 years. Its main deficiency was its packability: two of them won't sit well in our pot set, and so they end up on their own in the pack, and since I usually carry the kitchenware, that’s two more loose items in my pack.

Then, in a 2023 overhaul of our cooking system, I chose the S2S Alpha 2 Pot Cookset, which included a pair of mugs that nest one inside the other and thus fit nicely inside the smaller of the two pots—if you take off the foam insulating sleeves and lids and stash them alongside. What a concept! But they don’t hold as much as their predecessors, and the lid isn’t leakproof like the GSI, and those foam sleeves have an outer skin that rips and peels off with normal use and gets kind of gross, so—not the grail.

Now we are looking forward to another long hike this summer and accordingly trying to pare away some weight (my wife and I only getting older), we’re going to try to get by on a one-pot system that could potentially accommodate two larger nesting mugs. Enter the Passage (mug, that is).

Since GSI and S2S are competing for the prize, here are some stats (I gave the 1st gen S2S mugs to my daughter, so they are not represented):

For me, the Alpha is out of the running because I like a bigger mug and because the outer sleeve has deteriorated after a couple months’ worth of nights out, including on Sweden's Kungsleden. S2S seems to have abandoned the outer sleeve and now offers the similar but non-insulated 355 ml Passage Cup.

475 ml / 16 oz is enough for a big cup of coffee, followed by a generous helping of granola or oatmeal.

We can afford the 7 extra grams of the Passage over the GSI in favor of some of its other qualities.

The Passage mug is molded of dishwasher safe, BPA-free, glass-reinforced polypropylene. The double walls are separated by a thin air (or vacuum?) space, enough to give some insulation, with the two pieces welded together at a seam about 1 cm below the rim. We chose the orange and blue colors for him and her, respectively; a warm yellow is the third option.

I did a boiling water and kitchen thermometer test of the three mugs in the table above:

The GSI Infinity insulates better than the other two, but the difference is minor. With lids on, all three will keep a cuppa reasonably hot for a 30-minute sipping session. There is enough heat leakage through the walls for the Passage mug to double as a hand warmer on a cold morning.

The lids seals tightly with a ridged silicone o-ring. It has a sipping port and tiny breather hole, but unlike the GSI mug there is no closure, so it will leak if tipped over. One consequence of the tapered, stackable design is increased (relative) tippiness, so it’s best to pay attention to where you put the Passage down.

It does not have a handle, but that’s not a problem for me.

It has graduated markings molded into the interior wall, but (again unlike the GSI) these are very difficult to read almost to the point of being useless—it’s hard to get them to show up in a photograph:

With no outer sleeve and the lid and mug made of easily washable plastic, the Passage scores well on washability. The outer sleeves of both the GSI and the S2S Alpha don’t wash well. The fabric on the former tends to fray at the upper edge, requiring some maintenance, while the outer skin on the latter splits and peels off (photo in my updated review).

We’ll be taking the two Passage mugs with us on our long hike this summer, safely nested in our one-pot cook system:

The Passage Mug is not quite the backpacker’s grail. If we could add a completely spill-proof lid and more legible volume markings, and somehow teach it to pack up the tent, we might finally have it.

For me, packability is the main reason for choosing these mugs—it’s nice to have them stashed neatly inside the pot, with a canister-top stove and a few other items stashed inside, rather than rattling around loose in my pack. The superior washability is a plus. Solo hikers might be happier with the tried-and-true GSI Infinity, especially if it fits into a small soloist’s pot.

Background

I have lifetime of experience with backcountry cups and mugs of every description. I've use the Passage mug on a few outings so far, enough to recognize its limitations but otherwise be happy with it.