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Rapha’s Waterproof Rear Pack offers some excellent design ideas to make packing kit under your saddle less stressful, such as a two-part 'clamshell' harness and a tapered, vented dry bag. However, it scores a couple of own goals by having no rear light mount and no external bungee strap. Also, depending on how you use yours, getting it on and off could be a real challenge.

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Let’s start with the good stuff. Just as with their Waterproof Frame Bag, the Rear Pack immediately seems well-designed and solidly-made. It offers a semi-fixed rear clamshell-style harness into which you slide the specially-shaped Rapha drybag, and the beauty of this (rare) system is that when you stop at the café, campsite or work you can just undo the buckle, remove the drybag and walk away.

The harness works especially well because it's a semi-rigid plastic with an aluminium skeleton, so it's stiff and stays open – it's perhaps the easiest harness I’ve ever used. If you’ve not done much bikepacking it might not seem like much, but trust me, trying to pack your seat bag whilst it's attached to your bike is not fun. Top marks to Rapha for this design.

The aluminium skeleton also reduces sway, which is noticeable when out of the saddle on a climb. An external fixed frame would stop it completely, but this is certainly one of the less waggy designs, so thumbs up again.

The drybag is another surprise. It has two little slits which work like valves in other bags, but without the need to squeeze or tweak them. You simply stuff your kit in and roll the top over, while the trapped air is squeezed out as you press. Water doesn't get in because the slits are covered from above and water doesn’t run uphill. Ingenious.

I was sceptical at first, but I’ve yet to find any damp patches on my kit or puffer jacket (a great test item as it shows water easily). Rapha claim this pack is waterproof, and so far – not having hucked it into a canal and fully submerged it – I’d have to agree.

What’s not so good is the lack of a light clip. Yes, there are plenty of reflective elements, including a reflective closure strap you can leave to flap behind you, but considering some of the conditions these bags get used in I think a light attachment loop would be preferable. You can attach one to the rubber strap, of course, but unless the strap is really tight you might lose it, as I did. 

On a similar note, the lack of bungee straps or external loops means that stuffing your waterproof on the back when the rain stops is not easy either. Bungees offer so many uses – the stashing of waterproofs, flipflops, washing, your favourite social distancing pole etc – that I cannot see any reason for not having them on a bag like this. It’s probably because the upper case is molded and not sewn.

The biggest issue is the stitching on the seat rail straps, which gets gummed up with irony. Once fitted (itself potentially tricky), the strap won't tighten through the buckle because it catches on the little flap that's there to help you tighten it. 

This flap works well when packing as it naturally falls wide open, but we had three of us with tools trying to undo the straps and change bikes and it was almost impossible – even in a warm, dry office. It would be no fun at all after hours in the rain.

The issue is that the stitching on the tab splays just enough to jam in the buckle, especially once there's any weight in the strap. On the positive side, once fitted the harness is staying there, which makes it ideal for commuting and bikepacking. I have got more practiced and can now remove it without psyching myself up beforehand, but I've never had this level difficulty with any other pack.

With regard to its overall weight of 623g, it’s certainly porkier than Apidura’s Expedition 14l at 350g and costs £126, Ortlieb’s16.5l Seat-Pack at 456g at around £110 and the ‘bargain of the bunch’ Topeak’s Backloader 15l at 565g at £75. Only the latter has a stiffened frame to prevent sway but it's not as secure as Rapha's design. Revelate’s Terapin 14L employs the same style clam system and weighs 567g but costs more at £136. If sway is not an issue for you, there are other cheaper, lighter seatpacks.

So the Rapha Waterproof Rear Pack is a tale of two parts. It’s an excellent, durable design and one the best to stuff full that I’ve used, and if you're fitting and leaving it on one bike the harness is simple and secure. The bag itself is neat, easy to use and waterproof.

The other part is the lack external strapping and loops – perhaps due to the build, perhaps in service of that clean, simple aesthetic – and the tensioning helpers that don't help. Depending on your style, you’ll either find the Waterproof Rear Pack very good if missing a few 'standard' features, or so infuriating you might consider melting down your own bicycle just to get it off.

• www.rapha.cc

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