Sea to Summit Ultralight Spark IV

A wonderfully warm, compact and light winter sleeping bag – The Good: * High quality 850 fill power goose down for great warmth (-8 degree C at "Comfort") at light weight (880gm for regular size) * Lofts up quickly. * Packs down wonderfully small - though you'll need to buy a separate compression sack to achieve this. * Silnylon shell fabrics feel lovely to the touch and have proved surprisingly durable, given how thin they are. * Comes with separate storage bag to protect down when not in use. * Though it's hardly "cheap", it is quite reasonably priced given the specs and performance.

The Bad: * Sea to Summit use a locking zip on all their bags (that I've owned anyway) - they all seem to work in the most unintuitive manner and refuse to unlock when you're in a hurry to get out of the bag! Please, just use a regular zip! The zip also tends to catch on the ultra thin shell material though to be fair, all bags of a similar design do the same, you just need to be careful when using the zip. * Part of being a warm yet light/compact sleeping bag is a snug fit that minimises dead space/material and air gaps. The bag can definitely feel a bit constrictive if you're broad shouldered or just used to rectangular bags. * Does seem to have a tendency to form condensation on the top of the bag's shell fabric when it's cold. * This isn't the fault of a -8 degree C bag, of course, but unless you're a particularly cold sleeper or only camp at altitude, a seriously warm sleeping bag like this isn't going to be comfortable over the warmer months. Definitely a cold weather/snow camping bag only. (The less-lofted Spark II and III versions are better general purpose sleeping bags for most people.)

Bottom Line: For the money, the Spark IV (and its female equivalent, the Flame IV) is a high performing sleeping bag, with great warmth and low weight. Combined with an appropriate high R-value mat, it's a solid sleep system for winter trips in the snow and above the treeline.