Footprint advice?

Hello, looking for some advice on a footprint for a Big Agnus Copper Spus UL2 tent.

Looking to do something DIY, but basically don't know what material to choose.  It will be used on a 2 month trip in mongolia where I suspect we'll be camping at least 75% of the time.  So looking for something reasonably light weight, but durable enough to last use the trip.  Currently I made one from a Halford's Tarpaulin which is pretty much bomproof but weighs in at over 650g!!!

So any suggestions on where to look would be great.  Have read about getting some polycro from Lowes/B&Q but I have no idea how durable that stuff is and if it's suitible for day in day out use over 2 months.  Also read about using tyvek although I don't know what the equivilent is here in the UK or where to get it.  And finally have seen about Penning outdoors P2GR material (have calculated this should come in at around 300 grams) which seems like the heaviest and most expensive option but probably the most durable and at least is half the weight of my current footprint.

 Any help greatly appreciated!!!  thanks

the pennine stuff is bombproof/waterproof but heavy -

some off the shelf options here

 You could try stuff from the building trade called Tyveck.

 Very thin 'paper' like material, but very strong and light.

 Henry Shires of TarpTent uses it for his footprints, so I'd reckon it must be good.

 I've used it on top of heather and small gravel, without a problem, no punctures in groundsheet.

 Oops just seen Mole beat me to it!

 Paul.