Therm-a-Rest Parsec 20 vs Zpacks Classic Sleeping Bag 20F
In short: The Therm-a-Rest Parsec 20 costs $19 less; the Zpacks Classic Sleeping Bag 20F is rated 9 °F colder on the figure each maker publishes; the Zpacks Classic Sleeping Bag 20F saves 10.2 oz; the Therm-a-Rest Parsec 20 carries the bigger loft budget at 15.3k cubic inches; only the Therm-a-Rest Parsec 20 publishes a lab temperature rating at all.
| Spec | Therm-a-Rest Parsec 20 | Zpacks Classic Sleeping Bag 20F |
|---|---|---|
| Approx. price | ~$470 | ~$489 |
| ISO comfort | 29 °F | not published |
| ISO limit | 18 °F | not published |
| Rating on the label | 20 °F | 20 °F |
| Honesty gap | 9 °F | — |
| Rating standard | EN 13537 | manufacturer |
| Weight | 1 lb 13 oz | 1 lb 2.8 oz |
| Warmth per ounce | 1.07 °F/oz | — |
| Fill | 900 fill power down | 900 fill power down |
| Fill weight | 17 oz | 13.7 oz |
| Loft budget | 15.3k in³ | 12.3k in³ |
| Shape | mummy | mummy |
| Shoulder girth | 62 in | 60 in |
| Zipper | full | none |
| Shell fabric | 20D recycled nylon ripstop, DWR | 10D DWR nylon |
| Hydrophobic down | Yes | Yes |
| Packed size | 7 × 10.5 in | 6 × 12 in |
Shaded cells mark the row where one has a measurable advantage. Weight, thickness, girth and shape are left unshaded on purpose: heavier is sometimes tougher, wider is sometimes warmer, and calling a winner on those would be an opinion dressed as a measurement.
What each one does well, and costs you
Therm-a-Rest Parsec 20
- 900-fill down is the highest fill power of any mainstream-brand bag here, and it is what gets a hooded 20-degree mummy to 29 ounces.
- Published EN comfort (29 °F) and limit (18 °F) figures, so the rating can be checked rather than trusted.
- 62-inch shoulder girth is roomy for an ultralight bag — most of its weight class runs 57 to 60.
- Zoned fill puts the down where it lofts and skips the crushed panel under your back.
- Duck down is RDS-certified and treated with a PFAS-free hydrophobic finish.
- $470 is cottage-brand money for a bag made in Vietnam rather than a cottage workshop.
- 20-denier shell is not the most durable in the class; a 900-fill bag deserves care around campfires and rough granite.
- Only two lengths and no wide option, so a broad sleeper has nowhere to go.
- 900-fill down is the first thing to suffer from damp storage or a hot dryer, and this bag has a lot of value tied up in it.
Zpacks Classic Sleeping Bag 20F
- 18.8 ounces for a hooded 20-degree bag is quilt weight with none of a quilt's draft problem.
- Twenty-one size combinations across three girths and three lengths, each with its own published weight.
- Publishes target loft in inches, which is a more useful comparison between down bags than a temperature number is.
- 900-fill water-repellent down, made in Florida, with a shell weight listed separately from the down weight.
- Sewn-through construction means nothing to snag, nothing to jam and nothing to fail.
- No zipper at all — you cannot vent it, you cannot use it as a blanket, and you get in through the top.
- No ISO or EN rating; the 20 °F number is Zpacks's own, and the loft figure is the only checkable thing behind it.
- 10-denier shell is fragile enough that a tent-floor rock is a real risk.
- $489 for the middle size, and custom options push it higher.