well...regarding leaving the tent at home, lets just say that the weather up at 9,000-10,000 ft in the mountains is alot differant than it is in the flatlands of minnesota. i usually expect average winds of 20-30 mph with gusts up to 60 mph. last night top windspeed at 10,000 ft was 73 mph according to the avalanche experts. so lets just say a silnylon tarp would not be the best shelter for those conditions. a tent is a must have up in the alpine areas in which i like to camp for climbing, skiing, etc. i should also mention that our "summer" here usually only lasts a little over 3 months and the rest of the year snow is likely part of the equation..again, the need for a solid shelter is real around here. i have decided on the bd epic tents mainly for this reason. these tents are the lightest tent on the market that can handle mountain weather with ease. while i would certainly love to drop even a bit more weight, but the though of waiting out a torrential deluge/wind and hail storm like i experianced a fall or two ago in titcomb basin in a double rainbow or similar doesn't sound like my cup of tea.
as for my original thought of using the tarp as double protection, you need to understand that it doesn't rain here much in the summer. sometimes late in the season we get daily fast moving afternoon showers but they are usually come and gone within a few hours...well within the weatherstopping ability of epic. generally it is rare for us to get any prolonged periods of preceipitation, and if its in the forecast we usually hold off on heading up into the mountains anyhow. my thought is that if i am using the epic tent as a backpacking shelter for a week or so at a time a lightweight tarp could be used as double protection IF some type or prolonged precipitation rolled thru. generally though, we just want a lightweight (under a lb) tarp for kicking around camp etc since many times our backpacking trips involve some base camping at high alpine lakes for fishing or climbing. the epic tent doesn't have a vestibule and the stock one from bd weighs in at 15oz. i would much rather carry an 11-12oz tarp and have more fuctionality than a vestibule for cooking and stashing gear. it also leaves me the option of leaving the tarp and the extra weight at home for shorter adventures like overnight bivys for climbs etc.
all that said, back to materials...is silnylon actually lighter than epic? i always thought epic was the lightest wp/b type material out there other than the pricey guys (spinnaker, cuben). obviously as i have said before weight is more of a concern than waterproofing abilty since this will not be a shelter for camping. i also noticed that the tarptent sublight made out of tyvek is lighter than the one made of silnylon. was kinda hoping that tyvek might be a good fit due to its ease in obtaining and low price. anybody else got any ideas