This is a great, dedicated car camping bag, especially for folks that want a large, rectangular bag that doesn't include cotton fabrics. With all synthetic materials, this bag is better suited to extended camping when it might get wet. Unfortunately, it doesn't unzip to make a blanket, limiting its use for picnics or around the house use. The Celsius XXL earned average and higher scores in each of our metrics. The soft lining is comfortable on the skin and its over-sized design makes it the largest bag we tested. It's very roomy and appealing to see from afar, but after getting a closer look, we feel the bag's construction and quality have some room for improvement.
Performance Comparison

We like this bag's over-sized design and its shoulder baffles and adjustable hood.
Credit: Jason Wanlass
Warmth
We feel the Celsius XXL provided excellent warmth, but it did not perform as well as other 0-degree bags we tested. The soft lining is not flannel but is nice next to bare skin. This bag has unique features that contribute to its warmth. It has both a draft tube to back the zipper and a neck collar that can be adjusted to reduce airflow from the top of the bag. In addition, this bag has a sort of minimal hood feature which can also be adjusted tighter to secure a pillow or surround the user's head. With two layers of synthetic insulation - the upper one is sewn to the nylon taffeta shell fabric, and the inner one is sewn to the brushed poly flannel lining — this bag uses all the tricks to stop drafts.

Adjustable shoulder baffles allow you to cinch the bag around your neck, keeping outside cold air at bay.
Credit: Jason Wanlass
Comfort
The Celsius XXL version we tested is a generous 90 inches long (including the hood) and 36 inches wide. That's a lot of room for one person, but the bag is a few inches narrower than the most comfortable bags we tested. We enjoyed the feel of the brushed polyester lining.

Although not flannel, we still found the Teton's brushed polyester lining to be quite comfortable.
Credit: Jason Wanlass
Our one disappointment is that the zipper on this bag does not extend along the foot box, which prevents the user from unzipping the bag fully to act as a blanket. Overall, the bag's sheer size gave it a solid score here, landing it in the good company of a few other bags that scored in our top tier for comfort.

We were disappointed that the Teton's zipper doesn't continue around the foot box to allow the bag to be opened up flat.
Credit: Jason Wanlass
Features
The soft lining and draft collar are this bag's most notable features. Two large webbing loops sewn into the foot of the bag near the corners provide for easy hanging. The zipper closure flap secures on itself to hide the prickly Velcro. A tape backing for the zipper gave our testers snag-free operation, a plus for this product. We were also impressed with the bag's water-resistant shell, and equally impressed with Teton Sport's limited lifetime warranty. However, we were disappointed with the manufacturer's cleaning instructions, which specify hand washing only and laying flat to dry. The instructions also specifically state not to tumble dry, and that machine washing voids the warranty. We feel this is a negative.
Packed Size
This sleeping bag comes with one of the best stuff sacks of the bunch. It has compression straps similar to backpacking sacks, which also conveniently double as a carrying handles. The Celsius XXL is right in the middle of the bunch in packed size, and you could really cinch it down with the compression straps if space is at a premium.

The Celsius XXL compression bag allows the user to cinch it down if space is an issue.
Credit: Jason Wanlass
Value
The Celsius XXL lists at a reasonable price, and warmth and comfort contributed to a high overall score. These three create an above-average value when comparing what you're paying to what you're getting.

A super large design and fully synthetic materials are two of the Teton Sports Celsius XXL's top selling features.
Credit: Jason Wanlass
Conclusion
If you want a comfortable rectangular bag with all synthetic materials, the
Celsius XXL is a great choice. All synthetic materials are more appropriate for car camping in rainy places, and the Celsius XXL will dry much quicker than bags with cotton shell or liners. The Celsius' draft collar and shallow hood are unique features for a rectangular bag.