# How much colder is hammock vs. sleeping in a tent?

I just got my first hammock and am eager to try it out! I don't have an underquilt, I was planning to use my current bag and foam pad. In a tent, they would be on the lower end of comfortable for the anticipated low temperatures this week (~10-15F margin of the rated value, but I sleep cold). So I'm concerned that it would be uncomfortably cold in a hammock.

Is there a rule of thumb for converting sleeping bag temperatures into what it would "feel like" in a hammock, or how much of a temperature difference you feel on the ground vs. in the air?

• Very interesting question! (Sorry for silly comment :)) Commented Apr 27, 2017 at 20:13
• I use a sleeping pad (same as a for a tent) in my hammock and CBS isn't a problem. HOWEVER w/o the pad... yeah, it's real. Commented May 9, 2017 at 20:00

With a tent you would have protection from wind chill and unless you can cut the air flow to your skin some other way, the added effect of wind chill depends on the wind speed.

wind chill (F) = 35.74 + 0.6215T - 35.75V^0.16 + 0.4275TV^0.16

where T = air temperature (F) and V = Wind Speed (mph)

Pretty complicated, but it looks like the worst case is a temp diff of -20F or worse.

Anyhow I would guess it depends on the wind and the rain, if you have either then it will probably be too cold, you would need some cover like a rain fly at least.

• I decided to mark this as correct because I think it's the closest to an actual number I can get, the rest is just picking materials to mitigate the effect! Thanks for digging up the science behind it :) Commented May 1, 2017 at 18:22

It depends. Maybe colder, maybe not. (Yeah, right.)

Anyway, two major rules for hammock happiness:

(2) You must arrange your rain fly to block air flow.

Sleeping pads: Are normally 20" (51 cm) wide. The hammock will wrap around your body. Your shoulders and knees (and possibly your elbows, upper arms, hips and thighs) will contact the hammock wall at various points because of this, and though you won't lose significant heat due to this contact, it will drive you nuts and keep you awake all night. Also, a sleeping pad under you means that moisture can't escape. But just about any pad you can get ought to keep your bottom side warm for most spring-summer-fall trips.

Rain Fly: I usually sleep on a slope. I hang the up-slope part of my rain fly straight down, weighted by a trekking pole hung horizontally. (I sewed on a couple of extra tie-outs for this.) The down-slope side of the rain fly can be raised as much as I want for views. Since cold air flows down mountainsides, this arrangement defeats the draft.

Some means of blocking foot-to-head or head-to-foot breezes is necessary at times. Sleeping in still air significantly raises hammock comfort. Don't be fooled by sales photos of hammocks with their rain flies splayed out flat. That won't work unless you sleep so hot that you could just as well snooze naked in the dirt anyway.

A minor rule: Something over the top such as bug netting helps block draftiness, but that isn't enough for me. I add a piece of super-light fabric over that when needed. I once used some super-thin, super-breathable non-woven fabric that covered a scanner I bought. Don't know where to get more of it but it was great. The right weight of "interfacing" might work. Haven't tried it, but look here for some ideas: https://en.wikipedia.org/wiki/Interfacing and http://www.joann.com/fabric/utility-fabric/interfacing/

Suggestion: Try a few close-to-home nights outside before doing anything adventurous.

• Thanks for the tips! The hike I have in mind is pretty short, so worst case I'll be an hour from my car :) I wasn't sure about a rain fly since it isn't supposed to rain, but that's a good point about blocking the wind, may have to reconsider.. Commented Apr 28, 2017 at 1:00
• I did go out last weekend but the forecast went up, so I stayed plenty warm! I sew, so I'm familiar with interfacing - not sure I'd try that, it's not particularly weather-proof, more like a thin felt. I'm not sure what sort of fabric you meant, was it like reusable shopping bag material? Those are typically Polypropylene. Commented May 1, 2017 at 18:44
• Sleeping pads do work in a hammock to keep your underside warmer. I've used both the Therm-a-Rest Z-Lite closed-cell foam pads and the Therma-a-Rest NeoAir Trekker inflatable pads. Both work for insulation. Their width helps too-- since they are wider than your body they allow more room for your top quilt or sleeping back to loft around your body. Without something to push the sidewalls away a bit, the walls will naturally press against you, reducing any insulation-providing loft around you. Commented Aug 14, 2017 at 20:03