I think it's doubtful that a reflective thin foil membrane will stop any heat loss at all if it's beneath your ground sheet, as the heat loss will be from conduction.

Thin reflective foils work by reflecting radiant heat, which means that they require an air gap to work. This is why they are placed in the centre of Thermarest NeoAirs. If you place them directly under your mattress they could add to the insulation value as there will be the air gap of the mattress but as Louise has already pointed out you'll be in for a lively ride at night.

I'm not at all convinced that the thin films are likely to offer any significant protection to your groundsheet from punctures caused by sharp things beneath your groundsheet either - a thistle spine will just laugh at it!

As far as I can see, all a thin film - reflective or non-reflective - will offer is additional water protection from the ground, which is useful if your groundsheet is old and knackered and has a reduced hydro-static head. It will of course keep the underside of your tent a little cleaner, but you will still be faced with a muddy film to deal with each morning, which is probably harder to deal with than sponging mud off your groundsheet.

Spot on Alan - exactly why I pointed out that the stuff was 'advertised' as reflecting radiant heat.

However, if you check out the stuff I sourced you'll see that it's not smooth but finely dimpled. This has the effect of offering the *teensiest* bit of conductive insulation and a bit of radiation reflection by way of the dimples creating a slight gap between your mat (and cold bum). The benefit is certainly very obvious when camping on snow.

It's also *very* tough, thorns and other ******* things will ultimately puncture it - but it's another layer of protection.

The finish of the sheet is such that you don't slip and slide about....too much.

Louise

I carry a roll of this stuff at the bottom of my bag

http://www.lakeland.co.uk/8297/Slip-a-Grip-Non-Slip-Fabric-Shelf-%26-Surface-Liner---3m-Roll

A 180 x 30 cm length only weighs 125 gm and is very effective at stopping the overnight face plant into the wall of your tent.

If you take a roll with you but reduce the amount of chocolate you carry by just 5% there would be no increase in the overall weight of your pack.....

"If you take a roll with you but reduce the amount of chocolate you carry by just 5% there would be no increase in the overall weight of your pack....."

...cheeky!! :smile:

Hi
I use a piece of the material used to make sails for racing yachts. Very light and tough. It goes between the tent and Scotland with the hope it will protect my cheap tent. It also provides a table cloth to cook & eat on. So far it has worked. Also it is Bright Orange so I can use it to attract attention if needed - which I hope I never will. Cost was Zero as it was an off cut from the sail makers.
William

Bought a Sol - Survive outdoors longer - last week to try as an alternative to my silver reflective foil blanket. I like it. Certainly it is stronger, and feels more substantial. It’s 20g heavier than my foil sheet, but on first impressions 20 g is worth it.
The size at roughly 5 ft x 8 ft is ideal for the porch of the trookstar. Let’s see how it lasts over two weeks in Scotland acting also as a rain kilt and picnic mat.

I've bought a Tyvek sheet that I will cut to size as soon as I put up my tent and I can measure properly. So not sure yet how much it weighs.

Well, for what it's worth, in quite a few crossings I have never used anything under the tent inner. Actually, never ever on any tent. And never needed.
If on the other hand it is to use in a porch area, then that it totally different with a larger porch. And the double glazing film is super light and more than adequate.
If you are worried about a puncture leak, take some TENACIOUS TAPE. It is mighty stuff, and actually sticks to sil Nylon, unlike Duck Tape that is useless.

I use a ground sheet from Home bargains, £1,99 well worth the weight which is not much,👍