What the manufacturers say:

Now featuring Nikwax® Hydrophobic Down and a ThermaCapture™ lining for advanced, lightweight warmth, the three-season Antares HD can handle just about anything from early spring to late fall. It has also been updated with our new Zoned Insulation, adding a light layer of sewn-through insulation to the bottom of the bag. This helps reduce drafts when joined with your mattress, and frees you to use your bag in a hostel or your friend’s couch–wherever you don’t need a camp mattress. We do recommend outdoor use however. It’s just more fun that way.

Price: £420

• Zoned Insulation (Box-baffled 750+ fill Hydrophobic Down w/sewn-through insulated bottom)
• Reflective ThermaCapture™ lining for added warmth without excess weight or bulk.
• SynergyLink™ Connectors integrate your mattress for optimal comfort and efficiency
• Heat trapping draft collar and full-length zipper draft tube
• Differential cut maximizes loft
• Snag-free zipper
• Cinchable hood
• External zip pocket
• DWR-Treated 20D Nylon Shell
• Stuffsack and storage sack included

Thermarest Antares HD tested and reviewed:

The Thermarest Antares HD arrived for testing at the perfect time as early Spring and late Winter fought for supremacy. Being the first incarnation of Nikwax's Hydrophobic Down in a 3 season bag we'd seen it was hugely anticipated given the amazing results we'd seen in a Ran 4 season rated bag. In terms of warmth the down certainly didn't disappoint, although the Antares proved to be something of a mixed bag overall.

At a touch under 900g the Antares HD definitely qualifies as lightweight, though not the lightest for its temperature rating, and packing down to 7 x 12 inches it's not over-bulky. As is pretty much standard with quality down bags these days you get a mesh storage bag, along with the small bag into which it's just possible to squeeze the Antares.

The construction combines a box baffled upper filled with 750+ fill power Nikwax treated hydrophobic down with a sewn through, lightly insulated, underside. The reasoning behind this is twofold; When inside your bag you compress the insulation on the underside anyway and a growing use of insulated mats. In particular the Antares is designed to combine with thermarest's own NeoAir mats as a complete system, although other mats will work in the same way.

To complement the differential insulation Thermarest have equipped the Antares HD with a pair of straps on the underside through which the mat is guided, securing it in place directly underneath the less insulated side of the bag. When attaching the mat it's important to spread the starps out fully to apply even pressure over their contact area as they have a tendency to roll up and slide naturally into the join between inflatable mat baffles.

With a mat attached directly to the underside of the sleeping bag movement inside the bag is somewhat different and can take some getting used to. Rather than turning the bag with you, you now have to turn inside the bag. To allow this extra movement the Antares HD is cut quite generously, something you'll notice by the amount of bag overhanging the sides of a NeoAir XLite once attached. Whether or not the strap and mat system works for you may well come down to how you turn in the night; for me the straps were abandoned after the mandatory 3 nights to test the system. I found the required movement not to turn the mat with me too unatural. With the mat detached from the straps, however, I felt much more comfortable moving without falling off the mat.

The hood is nothing special but can be pulled in tight if necessary with one hand and the neck and zip baffles are efficient. The additional volume of the Antares means it can take a couple of minutes longer to warm up on the coldest nights but the difference is minimal and if allowed to loft for half an hour before getting in the 750+ FP down is right on the money for 3 season use.

The almost full length zip has, to date, proved snag-free and as the temperature has increased over the last couple of months it's been easy to ventilate. The box foot is warm enough down to -3 and as Spring moves into Summer the bag has the volume of fabric on the upper side to allow you unzip it almost completely yet still remain covered. This, perhaps, was the only configuration where I found the bag/mat straps to be a bonus, holding the base in place with the top open.

Overall the Thermarest Antares is a good 3 season down bag with the added bonus of Nikwax's hydrophobic down treatment. In terms of warmth per gram it's not cutting edge but part of that is down to the extra volume needed to accomodate turning without moving the bag itself. The idea of a thinner layer of insulation on the underside makes a lot of sense, particularly when the bag is matched with an appropite level of insulation in the accompanying mat, The straps, however, I'm not convinced by. One of the ealiest skills you develop as a camper is the ability to turn without falling off a mat and while I see the reasoning behind the idea with Zoned Insulation bags I'm not convinced the result is a better night's sleep - and that. surely, is the over-riding objective of a sleeping bag. The underside of the bag, without straps attached, hasn't proved particularly slippy on either the NeoAir XLite or NeoAir Trekker and there's a real temptation to take a pair of scissors to them. The saving grace, perhaps, is that we could see the system working well in a bivvy bag; something for a future test.