Nemo Forte 20F Synthetic Sleeping Bag | Tested and reviewed

Nemo always has an innovative approach to outdoor gear, and the Forte 20F sleeping bag is no exception, featuring nifty design touches and excellent sustainability credentials.

Nemo Forte 20F hanging over a gate

by James Forrest |
Updated on

If you’re looking for a standard mummy-shaped sleeping bag with decent temperature ratings, there is a humongous amount of choice out there. Our list of sleeping bag brands with such products feels almost endless: Rab, Mountain Equipment, Deuter, Marmot, Therm-a-Rest, Robens, to name merely six on our list of about 20.

But, if you’re after something a little different, US brand Nemo is known for its innovative and maverick approach to outdoor gear – and the Forte 20F is no exception. It’s a synthetic sleeping bag with a few unique design features, including a wide and roomy fit, a spoon shape for side sleepers, integrated vents and a weird-but-wonderful ‘blanket fold draft collar’. Some of these features may polarise opinion – will you love or hate them?

Ultimately we’d say the Nemo Forte 20F is a niche sleeping bag for side sleepers who need more room and tend to find mummy-style bags way too constrictive. Here’s the full lowdown.


  • Innovative design
  • Clever features
  • Roomy
  • Copes well with damp
  • Good for side sleepers
  • Sustainable


  • Too heavy and bulky for some hikers
  • Not as thermally efficient as a mummy sleeping bag

Temperature ratings

Nemo Forte 20F info on stuff sack

The Nemo Forte 20F has the following EN/ISO lab test temperature ratings: comfort -1C, comfort limit -7C and extreme -24C. These are solid stats for a bag priced at £225.

But, considering the roomy fit of the Forte 20F, particularly around the shoulders and knees, there is a risk of ‘cold spots’. You’re certainly not cocooned tightly by insulation in the same style as tapered, mummy-shaped sleeping bags. Consequently we’d take the -1C comfort rating with a pinch of salt and suggest mostly using this sleeping bag in slightly warmer climes.

If you need a lower temperature rating, the Nemo Disco 15 down-filled sleeping has a slightly improved comfort rating of -3C.

Insulation type, fill power, and fill weight

Nemo Forte 20F pillow holder

The Forte 20F is filled with Zerofiber PCR (100% polyester) synthetic insulation. This insulation is a 100% post-consumer recycled insulation, ensuring the bag has excellent eco credentials. There is a whopping 900g fill weight of this insulation in the Forte 20F and the insulation grade is a mix of 180, 150 and 100g/m2.

While it can’t perform exactly in the same way as down, the Zerofiber PCR synthetic insulation appears to have impressive qualities – it compresses down small, maintain its loft while you’re sleeping, and (as expected with synthetic insulation) keeps you warm in damp conditions.

Pack size and weight

Nemo Forte 20F in stuff sack

The Nemo Forte 20F clocks in at a weight of 1.55kg in the regular version and 1.68kg in long. This is heavier than ideal, but generally par for the course when it comes to synthetic sleeping bags. For comparison, the Forte 20F is actually 245g lighter than the synthetic, -3C-rated Robens Glacier III, but it’s also exactly double the weight of the ultralight down-filled Rab Neutrino 400.

For some hillwalkers, the 1.55kg weight of the Forte 20F will be too high and they will be forced to look elsewhere. For others, the Forte 20F will strike a decent balance between weight, temperature ratings and price.

The regular sized Forte 20F compresses down to a packed size of 46cm x 24cm, when packed inside the included stuff sack. This is bulkier than ideal and will take up considerable room in your backpack, but it shouldn’t cause any major issues.

Nemo Forte 20F stuff sack lengthways

For storage at home, a much bigger mesh storage sack (75cm x 35cm) is provided. Using this sack ensures you won’t ruin the insulation’s loft by storing the sleeping bag in a compressed state.

Materials and sustainability

The shell of this sleeping bag is made from a 30-denier 100% recycled polyester that is bluesign approved. The lining fabric is 100% recycled 20-denier polyester taffeta. Together these give the sleeping bag a soft and comfy interior, and both have a PFC/PFAS-free DWR.

As mentioned above, the insulation is also 100% post-consumer recycled. Consequently the all-round sustainability credentials of this sleeping bag are first-rate. Indeed, the Forte 20F is part of Nemo’s ‘Endless Promise’ initiative, which aims to keep gear out of landfill by ensuring products are mono-polymer (built from a single type of material) and fully recyclable at the end of their life.

In the USA you can request a return label from Nemo, post it back to them and they will sort out all of the recycling with their specialist partners. At the time of writing, this service isn’t available in the UK, but it will be launched later in 2024.

Size and shape

Nemo Forte 20F hanging over a gate

The key feature of this sleeping bag is its shape and internal volume. It is deliberately roomier than most other sleeping bags, with more space at the knees and shoulders for a less-constricted feel. If you like to feel tightly cocooned in a mummy-style sleeping bag, the Forte 20F is definitely not for you.

But, if you find mummy bags claustrophobic and restrictive, and you want more room to move around naturally at night, the Forte 20F might be your ticket to improved sleep in your tent. Indeed Nemo bills the Forte 20F as a “game changer” for side sleepers.

The extra space around the knees, elbows and shoulders is courtesy of Nemo’s so called ‘classic spoon’ shape, which curves and flares outwards, providing extra room where side sleepers tuck up their knees and stick out their elbows. This is probably a Marmite feature – some will love the extra room and find it super comfortable; others will find it too loose and potentially draughty. There is nothing particularly wrong with this sleeping bag for front or back sleepers, but it is clearly optimised for side sleepers.

The regular Forte 20F is suitable for anyone up to 183cm (6ft) tall. The shoulder girth is 150cm, the hip girth is 137cm and the knee girth is 152cm. The long version of the Forte 20F is suitable for people up to 198cm (6ft 6”) tall, and the shoulder, hip and knee girths are 167cm, 152cm and 162cm respectively.


Closeup of Nemo Forte 20F hood

You get all of the usual features you’d expect: a good adjustable hood, ¾-length left-hand-side zipper with draught-excluding zipper baffle, and a cosy footbox. But the Nemo Forte 20F is really known for its eye-catching and unique design features.

The first is an integrated, sleeve-like pocket for sliding in a camping pillow, such as the Nemo Fillo Elite Luxury Backpacking Pillow. This keeps the pillow neatly in place all night.

The second feature is what Nemo call the ‘Blanket Fold draft collar’. It’s a large, thick flap of insulation that acts as an external draught collar, rather than the normal internal draught collar design. The aim is that the external collar is more versatile – it blocks cold air when tucked in, or mimics the cosy comfort of your mattress at home when folded down.

We really liked this nifty feature, but – yet again – it may polarise opinion. Sometimes the insulated flap can ride upwards and cover your face during the night, which can be annoying, although this may not happen to all sleepers.

Nemo Forte 20F vent slits

The third unique feature is Nemo’s Thermo Gill vents. These are two 53cm vents across the top of the sleeping bag, with zippers on the top and on the underside. The vents never completely open, as there is always a layer of fabric between the top and bottom zippers, so you can’t stick your arms out of the vents, for example. But they are designed to allow you to micro-adjust your temperature inside the sleeping bag.

Unzip them fully, half or just a few centimetres to fine-tune your comfort and thermo-regulation. We never felt the need to use the vents during our tests, so on many nights the feature may be surplus to requirements, but it’s certainly a nice thought that you can extend the use of a 3-season bag into warmer climes without overheating.


The Nemo Forte 20F is an innovative, spoon-shaped sleeping bag with some unique features and a design tailored for side sleepers – but the extra room risks cold spots for some users.

How we tested

James Forrest navigating while testing gear for LFTO

The Nemo Forte 20F was tested and reviewed by James Forrest. James has been one of our freelance gear testers and feature writers on LFTO and our magazine, Trail, for the past few years.

James is based in the Lake District, is a prolific peak-bagger, and one of the most high-profile outdoor writers in the UK.

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