Here is how these two tents compare on the numbers. They score within a hair of each other, so it comes down to the details below.
| Big Agnes Copper Spur UL3 | SlingFin Portal 3 | |
|---|---|---|
| GearScore | 77✓ | 76 |
| Capacity | 3 | 3 |
| Packed weight | 54.0 oz✓ | 60.0 oz |
| Floor area | 41 sq ft | 41.5 sq ft✓ |
| Space-to-weight | 12.1 /lb✓ | 11.1 /lb |
| Peak height | 43 in | 44 in✓ |
| Doors | 2 | 2 |
| Vestibules | 2 | 2 |
| Price | $650✓ | $690 |
| Type | Ultralight | Ultralight |
Highlighted cells mark the better spec: Copper Spur UL3 in blue, Portal 3 in amber. A blank spec is never counted as a win. GearScore is the overall rating (0 to 100); re-weight it on the full tent comparison. Prices are current MSRP.
The Big Agnes Copper Spur UL3 against the SlingFin Portal 3 is a study in priorities. They are close enough that this really is about which handful of specs you weight most.
The Copper Spur UL3 is 6 oz lighter, better space-to-weight, and $40 cheaper. The Portal 3 is more floor area (41.5 vs 41 sq ft) and taller (44 vs 43 in peak). Their GearScores land within a couple of points (77 vs 76), so neither runs away with it.
Pick the Copper Spur UL3 if you care most about low weight and space-to-weight, which makes it the better call for counting grams on long miles. Pick the Portal 3 if floor space and headroom matter more to you, or you are focused on comfort and room to move.
The Big Agnes Copper Spur UL3. It is 6 oz lighter than the Portal 3.
The SlingFin Portal 3. It is more floor area (41.5 vs 41 sq ft) than the Copper Spur UL3.
They are nearly tied at 77 and 76 on the default algorithm, so re-weight the score to your own priorities to break the tie.
It depends on your priorities. Go with the Copper Spur UL3 for low weight, or the Portal 3 for floor space. The spec table above shows exactly where each wins.