Tent footprint for fastpacking: 18 g/m² - how to cut it correctly
When fastpacking, every gram counts, but a groundsheet has a clearly defined purpose: it separates the tent floor, mat, or bivouac sack from the wet and rough ground. XFOIL is designed for this purpose with a weight of 18 g/m², a thickness of 19 microns, and a waterproof, plasticizer-free polyolefin film.
The available XFOIL sheet measures 1.6 × 2.4 m and weighs 67 g. You cut it to the size that fits your sleeping area – nothing more. View XFOIL 1.6 × 2.4 m.
What the film can do – and what it can't
Underneath the tent floor, it keeps ground moisture away from the tent and reduces abrasion on the groundsheet.
Under a tarp or when bivouacking, it lies beneath the mat and bivouac sack. The quilt goes on top; the groundsheet does not replace a bivouac sack.
It is not a sleeping mat. Your own mat is still your only protection against cold and pressure points.
The film doesn't protect against everything. Check the storage area for thorns, sharp stones, and roots anyway. A thin groundsheet complements your choice of location, but it doesn't replace it.
The right cut
There's no universal standard size. First measure the area that actually lies on the ground, and then cut it to size. 84 × 210 cm at 18 g/m² is approximately 32 g – this is a calculation example for a narrow, single-person setup, not a requirement for every tent.
Solo tent and trekking pole tent
Use the groundsheet as a guide, not the tent's outer dimensions. The groundsheet must not extend beyond any side. For a trekking pole tent with a trapezoidal floor plan, it's better to cut the groundsheet to fit rather than leaving a large rectangular overhang. Visibly protruding edges can allow water to seep between the groundsheet and the tent floor.
Tarp and bivouac sack
Under a tarp or with a bivouac sack, a simple, rectangular layer under the mat is sufficient. Leave only the extra space at the head and foot ends required by your bivouac sack and sleeping position. Seams, grommets, and additional parts are unnecessary for this application.
Here's how to proceed
Set up your tent, tarp, or sleeping place on a level surface as a trial run.
For a tent, mark the groundsheet; for a tarp or bivouac sack, mark the mat and the required reserve.
Cut with a smooth edge and lay out the film once before each tour.
At the campsite, remove any sharp objects before placing the film and sleeping system on the ground.
Care, durability and storage on the go
At 18 g/m², the foil is intentionally thin – that's the price for the low weight, not a defect. Treat it accordingly as a consumable item and not as equipment for the entire trekking lifetime: Check it briefly for small holes before each trip, especially at corners and folds where the stress is greatest.
After your trip, let it dry briefly before packing it away – storing it damp and folded encourages creases in the same places, creating thin, brittle lines. When traveling, it's best to keep it flat or loosely rolled in your backpack rather than sharply creased, for example, alongside your tent or as a flat layer against your back – this way it will last for more trips.
The short decision
You sleep in the tent: the cut should be slightly smaller than the groundsheet.
You sleep under a tarp or in a bivouac sack: rectangle under mat and bivouac sack.
If you only want to save weight: Calculate area × 18 g/m², instead of choosing a cut by feel.
Conclusion
For fastpacking, a groundsheet is only useful if it fits the groundsheet or sleeping area exactly. Measure first, remove any sharp objects from your sleeping area, regularly check the groundsheet for damage, and only take the area you actually need.
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