Shelters are made from a variety of materials which have a variety of strengths and weaknesses.  One of the important properties of a shelter is being able to keep you dry. Many fabrics, even those that aren’t “waterproof” can keep you drive in moderate conditions. Just think about the materials used in many umbrellas. Storms though can be another story. According to Richard’s post, extreme thunderstorms can generate hydrostatic heads of 12k mm?!, and typhoons can generate 20k mm. Also note that placing weight in a concentrated place (like kneeling) can generate quite a lot of pressure. This is why conventional shelters often had a more waterproof floor than roof.In increasing weight:

• Dyneema (Cuben): spectra threads embedded between Mylar. Available in 0.36-1.6oz weights. Quite waterproof. Tear strength good (.6) to Excellent (1.6).  Roughly 4x the cost of sil-nylon. Does not stretch when wet.  Not the most abrasive resistant material. Sewing weakens material so best to be taped or glued.
• Spinnaker: tightly woven polyester which is silicone impregnated. Typically .8-1.1oz weights. Hydrostatic head typically 1400mm (same as sil-nylon). My field experience with spinnaker is that it is better than sil-nylon, and the the spinnaker used by MLD is indeed at least 30% better than any other spinnaker I have encountered.  I have experienced misting through sil-nylon and other companies spinnaker shelters, but I have yet to encourage conditions in the field where rain hits hard enough to mist through MLD spinnaker. In fact, hose with a high speed nozzle didn’t cause misting. Does not stretch when wet.  No abrasive resistant, be careful. Many people find this material noisy when it flaps in the breeze, but I have found that if tautly pitched the noise isn’t an issue.
• Sil-Nylon: tightly woven nylon which is silicone impregnated. Available in 1.1-2oz weights. High variability is waterproof. Richard suggests that it’s typically 1400mm but heavier weight such as used by GoLite can be close to 3500mm. Will stretch when wet or when the humidity increases so expect to need to retention. Silcone treatment makes the material strong than the nylon left by itself.
• Sil-Poly: tightly woven polyester which is silicone impregnated. These materials came on the market after a stopped following fabrics closely. Dan Durston explains why he believes Sil-Poly is significantly better than sil-nylon.
• EPIC: The Black Diamond  Epic tents used the Alpine Summit process fabric. It averages a hydrostatic head of 1,300 mm.
• Nylon eVENT fabric averages 28,000 mm.
• Conventional double wall tents typically use 70 denier urethane coated nylon with a 1 oz coating as the fly fabric. It averages a hydrostatic head of 56,275 mm.