SIG is a sewn in groundsheet, bath tub groundsheets come up at the sides to prevent draughts. Bath tubs will give better ventilation but a SIG might be warmer.
You can also get zip in groundsheets (ZIG) which gives all the benefits of a Sig but it can be removed.
We chose this option for our new tent (Outwell Bear Lake 600 which we are picking up tonight ... can't wait for Easter to try it out) as we go away for a few nights at a time and we like to roll back the groundsheet during the day to look after the grass as best we can.
Also with a SIG, if it gets damaged badly then the tent could need replacing whereas we could just replace the goundsheet, not sure of the cost but will not be £600 as it would to buy a new tent. And our groundsheet did get ripped twice last year.
Hope that helps
Pauline
Don't forget to leave a review of all tents you've used, for a chance to win fantastic prizes
Having used both over many years,we prefer SIG..probably as we do most of our camping in scotland and there are not many warm nights ,even in summer.We use a small fan heater and without SIG its a waste of time trying to heat the tent. Have to disagree with Pauline regarding damage to SIG,easily repaired using the right gear and worse case if SIG was totally destroyed..it then becomes a tent without SIG and you would just use a groundsheet,no need to replace the tent....regards john.b.
------------- It is a wise man who has something to say.
It is a fool who has to say something.
It is always sensible (although admittedly not always practical) to use a groundsheet protector or footprint, which is effectively another groundsheet under the main tent groundsheet. This method should be used whether you use a SIG, ZIG, it not only protects the main groundsheet from sharp stones etc. but also keeps it clear of mud and adds to the insulation from the ground.
Rob
------------- The Sun always shines on TV.(and not on my caravan!)
Don't forget to leave a review of all tents you've used, for a chance to win fantastic prizes