The Ion is very light bivi bag with an interesting large hood that has a wide flap fastened with Velcro tabs covering the entrance and a drawcord so the opening can be reduced to a small hole.
Most of the time just the flap is enough to keep out the weather and there’s no need to turn the bag upside down as with ones with just a drawcord. There’s room to store some gear in the hood as well. A winter sleeping bag plus sleeping mat easily fi ts inside but because the fabric is quite thin the mat would be better underneath to protect the bag from abrasion.
The weight is very low and the cost reasonable. However there’s one drawback and that is that the fabric isn’t fully waterproof. Described as “highly water resistant” it has a hydrostatic head of 1500mm, which is actually waterproof but only just. Much wear and the fabric will probably leak. Because of this the Ion is best used as a sleeping bag cover inside shelters or for emergency use and the very occasional bivouac.