Review: Therm-A-Rest Boost 650 Sleeping Bag

An adaptable 3-season sleeping bag packed with features to keep you comfortable in variable conditions. Perfect for any on-the-move adventures.

Therm-A-Rest’s Boost 650 sleeping bag is brand new to the UK market and it is an exciting addition to their range. Not only does it come in multiple length and width options, it features a WarmZip, which adapts the bag from semi-rectangular to mummy shape. The bag also has zippered arm holes allowing you to read, cook or ventilate without losing too much heat. The Boost 650 is a really clever, well thought out design.

Therm-A-Rest Boost 650 Sleeping Bag: The stats

Features of the Therm-A-Rest Boost 650 Sleeping Bag

Insulation and fabric

The shell and lining of the Boost 650 are GRS-certified 20-denier 100% recycled nylon. Exceptionally light and soft, the fabric still feels substantial enough that I’m not worried about tearing it. I like that the sleeping bag is made from light coloured fabric. This isn’t because I prefer the look of light colours, it makes spotting and removing any hitchhiking ticks or insects far easier and I’m more aware of when the bag needs a wash.

Featuring a PFAS-free DWR coating, the shell also helps protect the RDS-certified hydrophobic 650-fill down from any contact with moisture. Featuring zoned insulation, the down is thicker in key warmth areas: top of the bag, shoulders and core. For me, this does make the insulation on my legs feel a bit too light, even when the bag is converted to the mummy shape.

Shape

A great advantage of the Therm-A-Rest Boost 650 is the extensive range of size options available, varying in both length and width. You need a good fitting sleeping bag to maximise warmth, so having more than a couple of size options means it will suit a wide range of people. The Boost 650 is designed with a roomy semi-rectangular shape, featuring generous width in the shoulders, hips and footbox. As a side sleeper, I really appreciate this extra width and have found this bag the most comfortable I’ve ever used on warmer nights. For colder temperatures, the shape is converted from semi-rectangular to mummy by the Warm-Zip feature. The thermally efficient mummy shape still feels slightly generous in the footbox width from other sleeping bags I own, which means my legs still tend to feel the cold more than I’d like.

WarmZip

Designed to pull the 650 down fill closer to your body, the WarmZip converts the semi-rectangular sleeping bag to a mummy shape. The WarmZip section runs almost the entire length of the top of the bag with a two way zipper, giving control over where you want extra warmth. Closing the WarmZip can add up to 6ºC to the bag’s temperature rating.

Entry zipper

The left-sided YKK entry zipper of the Boost is sturdy and smooth running. Two-way for versatility, you can easily ventilate around your torso or feet. I don’t mind which side my entry zipper is on, but it only comes in a left-sided version, so keep this in mind if you have a preference.

Arm holes

By far my favourite feature of the sleeping bag is that it has zippered arm holes. Haven’t we all dreaded having to unzip our sleeping bag to grab something from the cold outside? With these baffled arm holes, you can unzip from the inside and reach out, losing as little heat as possible. Because of their draught-tube baffles, the arm holes also don’t let heat from the bag escape when closed. Cold mornings are a lot less brutal when you can reach out and make a coffee before fully emerging from the warm cocoon of your sleeping bag. Also a means of ventilation, the arm holes have dual functionality.

Hood

I really rate the hood on the Boost 650. It has a lofty fill, integrated draft collar and can be cinched very tight. During the coldest night I have so far spent in this bag, all that was peeking out of the hood was my nose and mouth! My head has never felt cold in the hood and it is very comfortable to rest your head on.

Packability

The Boost 650 comes with both a storage bag and stuff sack included. The stuff sack is good quality, allowing for a tight pack which doesn’t loosen over time. It is quite a long, narrow shape (regular size: 20 x 7.5 inches flat), which I find very fiddly to stuff. There are also only 3 compression straps, which make getting an even compressed shape challenging. I manage to pack my Boost 650 down to 11 x 6 x 6 inches, weighing in at 1.3 kg including the stuff sack weight.

Therm-A-Rest Boost 650 Sleeping Bag review

First impressions

Therm-A-Rest are known for quality kit and this sleeping bag is no exception. When I first opened the Boost 650, I was very impressed. Even just on inspection, the zips glided beautifully, the fabric was strong, but buttery soft and there were a tonne of useful features. The design seems innovative, with features that improve the functionality of the sleeping bag, rather than being gimmicky. I was really excited for my first night in the bag and it met my expectations beautifully. I had a sound night’s sleep with lots of room for movement.

Versatility

I use my sleeping bag in various situations: for bothy nights, in my mini-campervan and for wild camping. The Boost suits them all. Compared to other sleeping bags I own, it blows them out of the water when it comes to versatility and adaptability. The WarmZip design is very clever, and I feel like you almost get two sleeping bags for the price of one. It certainly feels like a totally different bag when you are in the semi-rectangular or mummy shape. I also now can’t be without the arm holes. It is a design feature that just makes sense. I use them all the time.

Warmth

I have debated how to word this section as I don’t want my opinion to be taken as a direct criticism of the sleeping bag. I personally find the Boost 650’s stated temperature ratings nowhere near where I would judge them. The ‘comfort’ rating is listed as 0ºC and the minimum stated temperature rating is -6ºC. I reach my lower end of comfort in this bag at around 3-4ºC. That is with thermal leggings, thermal socks, thermal top, mid-layer and thermal beanie on. I have to stress how personal an opinion warmth is. There are many other variables (e.g., how insulated your sleep mat is) which may influence how comfortable you are in a sleeping bag and certain people may just naturally feel the cold more than others. I have read up on how Therm-A-Rest rate sleeping bags and they themselves stress that temperature ratings are intended as guidelines to compare products, rather than any guarantee of warmth. Essentially, don’t take this as a criticism of the bag, more of something to be aware of when heading out in lower temperatures. Know your own body, test any new sleeping bag out before committing to cold nights and never take the temperatures rated on the bag as facts to rely on.

Pros of the Therm-A-Rest Boost 650 Sleeping Bag

The Therm-A-Rest Boost 650 is a very high quality sleeping bag. From first look, I could see that performance had been focused on when designing the bag. There are little features on top of the main ones I’ve already mentioned which make using this bag enjoyable such as an internal pocket big enough for a phone, external AND internal anti-snag pulls on all the zippers. Even though the fabric is soft and light, you can tell it is built to last and I use this sleeping bag confident in it’s durability. The arm holes are genius. I have had so many compliments and questions about the sleeping bag because of them. I was also the envy of my friends when I could stay in my bag whilst having my morning coffee in a cold bothy.

Cons of the Therm-A-Rest Boost 650 Sleeping Bag

The only downside I have found is that I find the Boost 650 to not be quite as warm as rated. Please understand that is a personal opinion and your own experience of the sleeping bag may be different. Something to keep in mind, rather than an objective ‘con’.

Verdict

I love the Therm-A-Rest Boost 650 and always look forward to my next night in it. It demonstrates exceptional quality and has lots of performance and comfort-enhancing features that make using it a pleasure. Sitting looking like a giant blue caterpillar, I enjoy nothing more than making my morning coffee from the warmth of my bag – the arm holes are a game changer! Taking note of my temperature advice, I really recommend this sleeping bag as one which will suit a huge range of people, weather conditions and types of trips.

The Boost is a first class piece of kit best for adaptability and versatility when facing changeable conditions across 3-seasons. It’s also light and packable enough to cover distance with. Available in sizes to fit a range of body shapes and heights, the Boost 650 is a high quality sleeping bag that will suit many people, and is built to last. I had excellent first impressions of it, which continue with use. Plus, it offers good value for money considering the range of conditions it suits.

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Disclaimer: Cool of the Wild received this product free in return for an honest review. We only recommend gear that we love from companies we trust and we are under no obligation to give a positive review. All thoughts and opinions are that of the reviewer and we are in no way influenced by the brand or company.

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