larger-than average bivvy sack?

[johndavidjr]

I have an OR (non-waterproof) sack on last legs. It compresses winter insulation due to needlessly small circumference. Yet is a fairly standard dimension. Why they can't add a few inches......?

 

Would making it 10% larger make it 10% heavier? There may or may not be a math puzzle here.

[bearbreeder]

depends on the materials ....

 

my ID microbivy weight 500g ... and equivalent sized bivy out of a different fabric could weight 300g ... etc

 

 

[robpatterson5]

I have a huge ID pertex bivy, 10-12oz ish and easily fits a winter bag and more. Great bivy but rarely use it in winter, if you have a skinny bivy I might see myself trading to save a few oz in the summer.

[OlympicMtnBoy]

Assuming your bivy sack is roughly a cylinder the back of my napkin says increasing the volume by 10% (increasing the radius) will only add about 5% to your circumference, so if you keep the fabric the same it should only weigh about 5% more. (had to stretch my brain there)

 

Of course your sack isn't quite cut like that and you may actually need a bit more than 10%, but I do know other bivy sacks have different cuts. Some of the smaller makers (Oware, etc) would probably do a custom job for a really puffy sleeping bag size too. I agree though, my OR gore-tex sack also compresses the foot area a tiny bit with my biggest bag.

[mountainmandoug]

Look at http://shop.bivysack.com/

 

They will do custom work for a reasonable fee, and there will definitely be people to converse with about what size the sack actually is and what you will need.

[G-spotter]

a garbage bag from walmart is functionally equivalent, and more appropriate for the contents

[johndavidjr]

G-Spotter:

I've used garbage bags a fair amount for sleeping. You need 2-3 & join them with duct tape.

 

However, you are unable to realize their actual utility, which is as vapor barrier liner, rather than as bivy sack.

 

Given your severely limited brainpower, you'd be unable to grasp the whole VBL thing, so don't please don't trouble yourself about this.

 

You'd almost certainly suffocate if you tried this.

 

After using both improvised and manufactured VBLs in very wide range of circumstances, I've lost interest without drawing any conclusions.

 

I detected no difference in utility between manufactured and improvised VBLs. Brands were "Glad" and something else.