Getting into a conventional sleeping bag with no zips is just too hard. You need a zip down to the waist level. But beyond this is another matter. There is a marketing message aimed at the young that having a full length zip means you can zip two bags tog
Getting into a conventional sleeping bag with no zips is just too hard. You need a zip down to the waist level. But beyond this is another matter. There is a marketing message aimed at the young that having a full length zip means you can zip two bags together. A great idea at first glance, but in reality a complete waste of effort and weight. People simply do not zip their bags together, except maybe in a hostel or similar. Why not? For a start, it leaves a great big opening at the top for cold air to get in. Turning over in a double sleeping bag becomes a major nuisance; sitting up to get a drink in the night becomes even worse. Many of us have tried this and discarded the idea quickly.
Another marketing message is that with a full length zip down the side and another across the foot you can open the bag out as a quilt. Well, get real. You just don't do this with your best bushwalking bag in practice. And doing it with a tapered bag means your feet are never properly covered anyhow.
All you need is a half-length zip. Many good bags go as far as a 3/4 length zip. If the bag you want has more than that, ask if the manufacturer can make you one in your chosen colours and size and with the length of zip you want. The good manufacturers will; skip the ones who won't assist.
The zip is not an insulator. Heat will leak out through it, especially in the winter. So the inside of the zip should have a generous filled baffle tube running the length. Some bags have dual baffles: one on each side of the zip. The baffle(s) should be positioned so it doesn't immediately snag on the zipper: a hard request in fact. Some manufacturers put some heavier material or tape on the baffle where it touches the zip to make it less likely to jam the zip completely, and this is a good idea. But generally you have to be a bit careful when operating the zip to avoid jamming. It gets to be automatic.
Some people claim you should lubricate the zip when you get it. Candle wax or a silicone spray has been suggested. However at least one zip manufacturer (YKK) recommends you do not do this: they say the lubricant collects dirt and actually increases the rate of wear. The message seems to be to keep the zip clean and treat it gently.
What sort of zip is suitable? It seems that we are a rough lot, so a fairly heavy zipper is usually provided. But we don't want it too heavy: we have to carry it. You can get both continuous coil and moulded zips, and both sorts are used. You can different gauges: #3, #5, #8, #10, in increasing size and weight. The #8 size is fairly common for a sleeping bag, but it is rather heavy. The bags I make use #3 zips: I just treat them carefully, and they last for years. The slider should be 'non-locking', or you won't be able to get out quickly in the middle of the night, and it should be 'double-sided' or 'double-pull' so you can open it from the inside and outside. This is normal. A cloth tag on the small pull is a nice idea.
You may see in many advertisements from manufacturers that they only use brand X zips (often YKK) because they are the 'best'. An interesting claim, and not one which has a lot of proof as far as I have been able to ascertain. There are lots of brands available, and one would have thought none of them could afford to let another brand get all that much better. I would be interested in seeing any information to the contrary.