When heavy duty marquee is erected over grass they can suffer from extreme condensation, this is due to the water vapour grass gives off. For this reason any quality marquee flooring should have a non-breathable layer fitted underneath, this prevents the grass giving off water vapour and thereby mostly avoids excessive condensation. Even when laying a wooden floor inside a marquee a non-breathable layer should be fitted first.
The covers on marquees are usually made from PE, poly/PVC or PVC.
PE (polyethylene) is the cheapest covering and is similar to tarpaulin material; it can be crackly to the touch but certainly has many uses in the domestic market. As with any marquee covering always ensure you only use material that is flame retardant to British Standards.
Poly/PVC is a thin material that is given a PVC backing to make it waterproof. It is rarely used in the manufacture of marquees now as PE is more cost-effective and true PVC is more durable.
PVC is now the most popular material for marquee roofs and sides. It is very durable and can be given a lacquer coating for ease of cleaning. PVC is usually quoted in grams per square metre (gsm) though this can be a little misleading. There are many many different qualities of 500gsm for example such that a good quality 500gsm PVC will often outperform thicker cheap 600-700gsm PVC.