question on thermals

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question on thermals

Postby trekker76 » Fri 21 Sep, 2018 11:17 pm

Thanks for any help from those in colder climes. I bought a pair of mid weight merino thermals and wondered about the fit. I bought my normal sizes, say xl bottom and xxl top, and noticed they are a stretch fit, aka near skin tight. Is this the normal fit for thermals? The main reason I got them is to augment a -1 sleeping bag (+4 comfort rating) on rare occasion I find myself at temperatures under 5 degrees here( local mountain top). Is the idea to usually wear another layer on top of these for them to increase warmth for sleeping? thanks for any replies to the above or general comments on the theory of thermals.
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Re: question on thermals

Postby Nuts » Sat 22 Sep, 2018 1:18 pm

Iv'e only ever seen people wear thermals skin tight. If you don't like it (Iv'e gone away from them) you'll find an insulated mid layer (down or synthetic filled) is almost as light and compact.. is easier to get on, more useful in being able to throw them over clothes (and can help dry out day-clothes in the pre-bed time...) and will boost the temps far more than thermals. Or even a light fleece mid-layer. Otherwise buy bigger thermals? they'll do the same job in your sleeping bag, as far as I know, still all designed stretch-fit.

PS.. Maybe besides some of the heftier military grid fleece 'thermals'. More a mid layer in Ozzie mtns. I have a set of these (pant/top):

https://www.ebay.com.au/itm/New-USMC-Mi ... 2749.l2649

Loose fitting (for size) and super comfortable but relatively inefficient still.
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Re: question on thermals

Postby Aardvark » Sat 22 Sep, 2018 1:49 pm

The qualities that make a thermal are : 1. the type of fabric. ie Silk, Wool or a synthetic (polypropylene, polyester or similar - a petro-chemical, essentially plastic. It's a monofilament fibre. That means it does not absorb or hold any moisture. The fibre that is.) Cotton on the other hand is porous and will absorb moisture. Wool will also hold up to 30% of its weight in moisture but it has a property called heat absorption. It can help generate heat.
2. the weave of the fabric needs to assist in the movement of the moisture to the exterior (wicking). This is a hydrophyllic process. Body heat will generate a gas initially. ie Water vapour. A gas has smaller molecules but as they cool they will bind together to form a liquid. This needs to appear on the exterior of the weave to allow evaporation or movement through the next layer of clothing.
The simple fact that the fabric will wick means what is against your skin is drier. When your skin is wet it will lose up to 240 times more body heat than when its dry.
This is why a thermal is traditionally a skin tight layer. If the fabric is convoluted over your skin then it doesn't maximise the movement of the water vapour.
A second layer needs to be a bit more accomodating. These days the choice of thermals is almost unlimited. Anything that is synthetic is arguably a thermal. Regular synthetic shirts can act a layer.
I have something like 100 thermals of many types and makes. Some are sold as thermals and are specifically a loose fitting type synthetic shirt.
Polypropylene or similar nylon like fabrics are generally the cheapest and a good start point for most people. They are the skin tight type usually and provide a degree of stretch. Silk tends to be the most expensive. They usually have the advantage of minimising body odour, drying fast and providing the best heat to weight ratio.
Wool is a good option for many but not necessarily cheap. Can be scratchy if not the finest merino wool. Perhaps not as durable if fine merino wool.
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Re: question on thermals

Postby trekker76 » Sat 22 Sep, 2018 3:58 pm

Thanks folks much appreciated. I think what would serve me then is ditching the thermal top and just getting a mid layer I can use as a bit of an all rounder, aka can also use it as a pullover for day trips in winter here.
Nuts can you clarify the product you linked, is that what you suggest as an example of the type or something different, as you said it is 'ineffecient'?
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Re: question on thermals

Postby Mark F » Sat 22 Sep, 2018 4:42 pm

Using a set of thermals to use as pajamas at night is a great way to minimise sweat and body oils getting into your sleeping bag. For my walking, mainly Koscuiszko, ACT and Tasmania, the thermal bottoms are also used for very cold and windy days under my shorts. For this I tend to prefer polypro rather than merino due to almost zero absorption of water (fast drying) and greater durability but understand that merino will be slightly warmer for the weight. On top I like a merino zip neck top if planning to use it during the day - usually in autumn/spring. if it is just for night/camp wear then I use a lighter crew neck top - either polypro or wool.
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Re: question on thermals

Postby Nuts » Sat 22 Sep, 2018 5:14 pm

Just an example of looser fit 'thermals' trekker. I think they are a base layer in USMC terms. Too warm to walk in in most weather and a bit light as an insulation layer..


Personally (starting to rely as much on memories lol) I like to walk in lightweight long pants and a synthetic hoody as light as the season. I have a pair of synthetic insulated pants with a resistant shell and long zippers and a lightweight synthetic insulated jacket (hoody). Sometimes i'll wear them to start walking. Otherwise, instead of needing to get changed to warm up these go over the top. They usually dry out the damp day layers by bedtime, if I wasn't with a group i'd just use some combination of these to sleep in, (and use either a +4 or -1c sleeping bag over 3 tassie seasons.. otherwise take thermals (as well.. such as the USMC top)
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Re: question on thermals

Postby trekker76 » Sat 22 Sep, 2018 7:02 pm

Ok thanks Nuts. Any suggestions on decent lightweight synthetic hoody brands? The problem with being a hot climate creature is you don't even pay attention to the terms most of your life.
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Re: question on thermals

Postby crollsurf » Sat 22 Sep, 2018 7:32 pm

I've moved away from thermals and now prefer a liner. In particular a S2S silk liner weighing in at 100g, a lot lighter than thermals. It doesn't give any real thermal value but with a quilt, it helps with drafts and removes the feeling of the mat. I find it the next best thing to sleeping at home.

Thermals are just a bit... I don't know, clingy. Much nicer sleeping in the nuddy plus a liner keeps your bag/quilt clean, not that I care to much about that.

Probably equally or more important is the R value of your mat.
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Re: question on thermals

Postby Nuts » Sat 22 Sep, 2018 7:49 pm

You mean as a walking shirt? I recently bought a montane allez but find it a bit clingy, bought a patagonia sun hoody in the U.S but found it kind of plastic-y/ hot. I keep going back to Orvis's Hoodie.. they are a fly fishing outfitter. It's got some cotton so is a bit slower drying but quick enough. They are loose fitting, airy and hold up well if you do end up sleeping in them.

PS. Yes agree, unless you are planning on cold weather walking, a silk sheet may be more comfortable &/ or quilt.

In colder weather a similar synthetic hooded jacket , eg. patagonia bivy /hoody works well with the hoodie. Nothing is as light as carrying more sleeping bag but these have everyday function v's warm bag you may not need them 'most of the time'.
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Re: question on thermals

Postby crollsurf » Sat 22 Sep, 2018 9:47 pm

Nuts wrote:You mean as a walking shirt?...

Not sure if that question is directed at me but No. I just wonder if thermals are of any value if all you use them for is sleeping. However I have tried a fishing shirt in the past and they are pretty good except they are baggy under the arm. They get clammy under arm. Nothing a Merino T-shirt couldn't fix though and I still have that fishing shirt as backup.
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