Cycling UK Forum

On the dry bag thread the topic of putting your mat under the groundsheet of the tent came up. To be honest I'd never considered doing that with my mat. The mat I use (a Exped Synmat), is pretty think (approx 7.5cm) and I suspect this would be a big hump in the ground sheet and may impact how the tent pitches. I'd also be a little worried about exposing the rather thin looking mat fabric directly to the ground. I've never had any issues with condensation under the mat (one of the advantages of placing it under the tent), but I'm always interested in finding better ways to do things. So what do you folks do? Anyone place a SynMat (or similar thick air bed style mat) under the tent? If you do how well does it work, what are the advantages?

Thanks

Andy

It rather depends on the relative prices of your mat and tent. My mat cost appox £3 twenty years ago.
So it doesnt matter. The tent is new and expensive.

Though as the mat is normally smaller than the groundsheet you end up with BOTH wet and dirty, so generally it makes sense to put it inside the tent to avoid this.

I'm afraid I can't get my head round the idea that one buys a very expensive lightweight tent with superthin groundsheet and then puts a footprint or whatever under it (= extra weight...). That tent is not lightweight if it needs anything underneath. Personally I think groundsheets are far too thin for the job. That's why I like my Force Ten.

Two explanations for that.

First, you have to carry a sleep mat anyway, so it is no extra weight.
Secondly, One tent with two roles in life. Lightweight mode without footprint. Mediumweight mode with a "footprint" (old shower curtain or army IPK in my case not a £45 job).
The footprint is easily and cheaply replaced unlike a heavy duty fixed groundsheet.

horizon wrote:I'm afraid I can't get my head round the idea that one buys a very expensive lightweight tent with superthin groundsheet and then puts a footprint or whatever under it (= extra weight...). That tent is not lightweight if it needs anything underneath. Personally I think groundsheets are far too thin for the job. That's why I like my Force Ten.

I always use a groundsheet whichever tent I use. Weight is not a factor to me. Last time I used the tent was in a very muddy campsite in Belgium, packed tent and groundsheet in separate bags groundsheet got washed, tent is still as new.

gloomyandy wrote:So what do you folks do?

Mat inside tent, boxers/y fronts inside trousers.

I use a Thermarest Prolite 3 and more recently a Thermarest NeoAir. I always use them inside the tent, I've never had a problem with condensation under the mat, at least not that I've ever noticed.
I use a CTC bike bag as a tent footprint when touring abroad. For touring at home I use a home-made footprint cut from a cheap piece of tarpaulin from Wilkinson's. Adds a couple of hundred grams to the weight of my Terra Nova Laser Competition but I would rather that than risk wrecking the tent itself.

meic wrote:Two explanations for that.

First, you have to carry a sleep mat anyway, so it is no extra weight.
Secondly, One tent with two roles in life. Lightweight mode without footprint. Mediumweight mode with a "footprint" (old shower curtain or army IPK in my case not a £45 job).
The footprint is easily and cheaply replaced unlike a heavy duty fixed groundsheet.

I think the idea of a separate additional ground sheet is a good idea (I too used my bike bag, itself an old groundsheet, in Spain and this had a layer of bubblewrap in it ) and it does, as you say, provide flexibility. But I don't think this was what was intended/advertised by the makers of very lightweight tents, even though many are now offering footprints. I think it's that I object to. I also have a Jetpacker which I rate highly but to add another groundsheet does defeat some of the purpose, I would have thought.

Just to answer the OP, there is a condensation risk but putting the mat under the tent is like sleeping outside because the night is chilly.

My mat goes inside the tent for many reasons, one of which is that I don't fancy having to get out of bed and go outside in the rain to shove it over a bit if it's not quite in the right place.

Until I read this thread I had never even considered or heard of putting the mat under the groundsheet - my mat is an important part of my sleeping kit - it does not get deployed until I am ready to doss down - ditto sleeping bag (probably why they are both 15+ years old) - a little bit of condensation in the morning under the mat is no big deal - gone by the time I have finished packing

Okay, I'll declare my allegiance with the minority. My mat always goes on the outside of the groundsheet. It helps keep the groundsheet clean, is cheaply replaced when it gets too dirty, can be carried on the back of my bike without needing to go inside plastic bags (if it rains and it gets wet it doesn't matter), and to be honest I find it doesn't shift around in the night anywhere near as much when it's on the outside, especially if I'm on a slight slope. The slight dampness of the ground - or, more likely, its roughness - gives it a bit of extra purchase.

Hi Chris. What sort of mat do you use?

It was me who suggested this to gloomyandy in a different thread, but I think it was Copernicus who first came up with the idea of having the sleep mat below the groundsheet to avoid condensation. The science was on his side even if the populace wasn't. People have put forward all sorts of reasons over the years for why you can't do it (eg dirt on mat, theft of mat, inevitability of puncture of mat when unprotected by groundsheet, utter impossibility of reinflation of mat whilst in tent) but I have had many years of sub-groundsheet Thermarest and now Numo use, without these (or any other) problems. If you want to reduce in-tent condensation, try thinking outside the bathtub. If you don't need to or don't want to, have your mat in the tent. If it's a thermarest, whatever you do make sure you observe the "Sleep This Side" sticker.

hufty wrote:If it's a thermarest, whatever you do make sure you observe the "Sleep This Side" sticker.

I've always wondered about that. What happens if you don't?

alicej wrote:

hufty wrote:If it's a thermarest, whatever you do make sure you observe the "Sleep This Side" sticker.

I've always wondered about that. What happens if you don't?

Didn't know the answer either so looked on their site.

Sleep on the side with the logo. It is made of our nonslip fabric to ensure that even with a slippery sleeping bag, your mattress stays under you all night long. The bottom is generally a more rugged fabric that adds protection from punctures and abrasion. Some of our mattresses also come with small urethane dots on the bottom to prevent them from sliding around during the night.

http://cascadedesigns.com/Therm-a-Rest/FAQ