Is there a palce for Pertex Microlight in sleeping bags?

[Pedro Arvy]

According to current wisdom, Pertex Quantum, or a similar material, is the outer fabric of choice in a sleeping bag within a bivy or in a tent. And if you are in really wet exposed conditions for a few days, perhaps Epic might be used.

That leads me to ask, is there any place for an in-between material like Pertex Microlight?

Is there anyone on this site who strongly recommends Pertex Microlight over other outer shells?

[John S.]

Big Agnes has been using it for years.

[Roger Caffin]

I made my own sleeping bags with it.

[Pedro Arvy]

Roger,

Why have you chosen PM over more breathable materials?

And why do most products that BMW make use the more breathable Pertex Quantum?

I am not saying other products aren't used, I am asking, at the top end of the debate, why should they be preferred.

Take this quote from A Lightweight Guide to Backpacking in Sustained, Cold Rain:

Do not get a bag with a waterproof/breathable shell. Waterproof/breathable shell fabrics are a bad idea for down bags in humid environments as they impair critical air transfer and breathability, essential for drying the bag's insulation from insensible perspiration and moisture from wet clothes worn in the bag. The shell of the bag should be a light fabric that is highly breathable with excellent water resistance (e.g. Pertex Quantum or Microlight or polyester microfibers).

OK, this mentions PM, but why wouldn’t you go with PQ given the reasoning above

[John G]

I think PM provides extra insurance over PQ when using a tarp without a bivy, or a tarptent in windy blown rain (assuming the windy rain suprised you and you hadn't pitched your tarp / tarptent close to the ground on the windward side). PM should also be better for restless sleepers who brush up against the side more frequently. Also, at 1.3 ozy PM should be a little more durable than PQ's 1.0 osy for people who may be sitting on their bag and sliding around as they enter / exit the tent, get dressed, cook, etc.

For all 3 reasons, I'm planning on making bags/quilts for the kids using PM. PM's lesser breathability is a good trade off for the extra moisture protection for them. I'll use PQ for mine since I sweat more (even when cold) and don't rub against the sides of the tarp / tent very often.

[Roger Caffin]

Hi Petras

> Why have you chosen PM over more breathable materials?
You will laugh at the answer.

I was chasing some samples for gear development many years ago, and at that time the Quantum supply was very chancy: it was a bit too new. I was advised that the Microlight was readily available, and was given a couple of small (several metre) lengths. Since the stuff was so hard to buy in any quantity at that stage, let alone short lengths, I happily accepted the samples!

That said, the Microlight has proven to be very good. The shells for the sleeping bags I made with it weighed 250 grams each – not bad. Hoods were included. I put in 300 g of 800 loft down, for a total of 550 g per bag.

My wife and I used these bags for three months continuous walking last year in France, and they show no wear from that.

We have used them at -7 C while wearing thermals and socks and been warm enough. That might sound like an extreme claim, but 'combined tactics' for the two of us had us snuggled together and the two bags laid, one on top of the other, on top of us as quilts. Yes, 'quilt management' was required when we turned over, but it WORKED. No, we had not expected sub-zero weather when we planned the trip, but in the mountains anything can happen.

As to why Quantum is preferred by some? It is a bit lighter.

[Pedro Arvy]

Let’s get a bit more scientific about this.

Imagine a sleeping bag made of PQ which has been exposed to moisture.
Let’s say it absorbs 10 units of water.

Now let’s imagine a sleeping bag made of PM under similar circumstances. It will absorb slightly less water, say 7 units.

Moisture comes from your sweat and how much external water gets on the bag from condensation, rain splash and humidity absorbance.

No let’s consider how these bags dry. Drying occurs from body heat when you lie in the bag and when you lay it out to dry in the sun.

Because the PQ breathes better, it should expel water faster than the PM. Say 3 units per hour. While the PM expels water at say 2 units per hour.

Some of this drying is occurring because you are deliberately spending time drying the bag in the sun. The rest of the drying is occurring when you sleep in the bag.

I guess this means that the moisture absorbed by a bag depends on the drying time you can give a bag between sleeps if sleeping alone cannot dry the bag.

There are many variables here:

1. How much water PQ absorbs compared to PM
2. How damp the environment is
3. How much drying time you have
4. How fast PQ expels water compared to PM

This argument could be taken further to look at Epic and so on.

I was wondering, has anyone done measurements like this?

Or is the recommendation of PQ based on real world experience rather than such scientific studies?

I am looking at a custom Nunatak bag at the moment with 2” loft for use in a tarp tent and am sort of leaning to PM over PQ. I have a PQ bag with a good DWR and it just seems to take in moisture too easily for my liking – all based on my rough observations of course.

[Roger Caffin]

Hi Petras

One could argue about this until the cows come home, and part of the reason is because there are so many uncontrolled but significant variables. However …

> 1. How much water PQ absorbs compared to PM
More important might be how water does either absorb relative to the filling. I don't think either fabric holds much.

> 2. How damp the environment is
And infinite are the variations here

> 3. How much drying time you have
It is not just the drying time, but also the exact drying conditions – especially the ambient RH, wind speed and solar heat flux (for instance).

> 4. How fast PQ expels water compared to PM
Um … I don't quite understand this one.

> I was wondering, has anyone done measurements like this?
Enough work has been done to my knowledge for me to say that the whole subject is a minefield, wide open to manipulation by marketing departments.
Sorry.

[Pedro Arvy]

So Roger,

If someone gave you a free sleeping bag, the only sleeping bag you'd ever be able to use again, would you pick PQ or PM?

[Lynn Tramper]

I'm not Roger, and I haven't much experience with the PM. BUT I do have experience with the PQ, and compared to every other fabric I have used, the Quantum seems the least resistant to down leakeage. This is nothing scientific, just personal experience. So if I were an incurable 'gram weenie' I would go with the PQ, otherwise I suspect the PM might make the better 'only ever sleeping bag'.

I always carry a bivy bag, so in many ways the water-resistant/breathable arguement is a non-issue. I would avoid at all costs stuffing a wet sleeping bag (down or synthetic) if at all possible and go with a separate bivy option anytime the temp plummeted or the humidity rocketed. But that's not exactly UL….

[Roger Caffin]

Hi Petras

> If someone gave you a free sleeping bag, the only sleeping bag you'd ever be able to use again, would you pick PQ or PM?
Dunno. Not enough experience with PQ. The PM has been very good.

However, the comments of others against PQ certainly gives me pause. Combine that with the way my wife hates finding bits of down (usually small feathers, actually) floating around in the tent – well, …

SUL is not a mystic nirvana. I only go as far as I need, and no further. I like being comfortable.

Cheers
Roger

[Thomas Travis]

Does anybody know of a retail source for Pertex Microlight?

Tom

[Bill Fornshell]

I have a Western Mountaineering (WM) – Mitylite Down sleeping bag with PM. This is the model that opens more or less flat like a quilt. It is rated about 45 degrees. I have used it to sleep under on my bed almost every night this past winter so I can keep my heat turned down to 50 degrees.

I am a bit disappointed that the PM lets to many of the Down feathers through the shell material. I am also disappointed in WM for the amount of feathers in my Down. I don't know where WM gets their Down from but the Down I buy from Thru-Hiker.com is light years better than what WM uses.

I have used a lot of PQ in my MYOG projects and would take the PQ over the PM any day. Pertex designed Quantum to be their light weight Down proof material.

[Author]

Posts