Adding loft to my down bag…

You can add down to a cheap sleeping bag, but at some point you realise the cheap shell may be far too heavy.

That said, the only way to gain experience is to try doing it. Doesn't cost much. Go for it.

But do it inside a proper tent or a very large plastic bag. Outside the breezes will blow the down everywhere. Inside the down will go all over the house. You have been warned! :-)

My knowledge of sleeping bags is very limited but, I heard the only way to increase the temp rating is to increase the loft. For example, going from 1 inch of loft to 2 inches of loft. By using a method of over filling your sleeping bag, it sounds as if it would only maximize the amount of loft that you currently have. This may increase the temp rating by five degrees or so but not the 15 degrees that you are looking for. But again, I don't know enough to say for sure. I would certainly be intrested in hearing if your idea does work (I hope it does). Good luck.

If the bag has parallogram baffles then they will expand with more fill making the bag warmer (and shorter). If the baffles are vertical you'll get round tubes of higher loft pinched thinner by each baffle. Either way the down may not loft freely. Carefully ripping open each channel will take longer than filling and closing each channel. If the design has a side block, make sure you add down to the top, otherwise it doesn't matter which end you open up. I've repaired a couple of friend's bags. As long as baffles aren't torn out, it improves the bag's condition, but those folks didn't care about weight and at the time I had plenty of 600 fill down to use. I'd say go for it.

i checked the bag out again and it appears to be sewn through. no baffles. i think this might lead to cold spots no matter how much loft i add. it doesn't matter too much as it is because it's a 40 degree bag. i'm now questioning whether this mod would be effective…
so much for trying to be a cheap b*stard.

There may be a simpler answer than restuffing your bag, that many have used before: An overbag. Go out a buy / borrow a lightweight bag to put yours inside of.

Being in the Phoenix area, a 40 degree bag is good virtually year around, but when we head to Flagstaff, you may need a 0 (or lower) bag.

We use a very general rule of thumb for most of the kids in our Scout troop to help them pick the right combination: Subtract the temperature rating of the second bag from 65 degrees F, then reduce the rating of your bag by that amount. That is roughly what the bag is good for (YMMV).

The new virtual rating = (Your bag rating minus (65 F minus overbag rating)) (which also = add rating of both bags then subtract 65).

In this instance, two 40F bags gives you a virtual rating of 15 F. We've used this combination several times in 10 – 15 F weather.

I hope that helps.

MikeB

Mod?
Maybe, but you need to figure some things out first.
1) Is it a sewn-through bag or does it have baffles? Few 40 degree bags are baffled. Make sure. If it is sewn through, you would be better off with another bag.
2) How stuffed is the bag now? When laid out and given a chance to fully loft, does it puff up between the baffles? If it is already fully lofted there is nothing you can do to improve its temperature rating. If the bag is underfilled, you can improve the comfort range slightly. However, you will not get the bag down to 25 degrees no matter what. There is not enough slack in the system to double the loft, and that's about what it would take.

In the slim event that you actually decide to try this, most people who make down gear just go by feel. A handfull of down is not very much and you can just stuff here and there, moving it around as needed until it feels right.

Best advice: watch the after-Christmas sales or consider Mike Barney's idea of double bagging.

> it appears to be sewn through. no baffles. i think this might lead to cold spots no matter how much loft i add
Yep, right on. If it is sewn through, you can't do very much.
Maybe we have saved you some wasted effort?

yeah, i pretty much decided to pony up for a WM bag or something and just use this in the spring/summer. the lack of baffles is the deal breaker. thanks all for your input.

I have a Ray way 40 degree quilt and a 30 degree bag …. For cold weather I toss both into my Bivy, zip up the bag under the quilt, and wear a warm hat to bed. 23 oz quilt, 23 oz bag, and 7 oz bivy = 53 oz, or 3 1/3 pounds … not ideal, but I haven't saved up enough for a Montbell Exp yet.