How hard is it to make a pyramid shelter?

Narrow rolled hem (stitch ~ 1/4″ from edge) as Jerry describes, with one line of stitching.

I’m making a very similar pyramid (9x9x5), and decided to go with 1.1oz SilPoly. Was there any consensus on a good amount of depth for the cat curve for the corner edges? I was going with 3″, but am considering 2″. I’m also considering putting a 1″ cat curve along the bottom four edges, but maybe that is just ridiculous. Thoughts? THANKS!!!

Kyle, did you wind up making your 9x9x5 ‘mid?  If so, what cat curve deflection did you use?  I too intend to make either a 9×9 or 10×10 out of Silpoly 1.1 and was leaning toward no cat curve at all with this material, or at most something minimal like 2″

another question is how much does the silpoly stretch

for example, if your pole was 60 inches tall, and the mid was 120 inches wide, then it would be 60 inches from the pole to the side.  If the silpoly didn’t stretch, you’d want it sqrt(60^2+60^2) long (= 84.85 inches).  Assuming there’s no gap between the edge of the tent and the ground.

should you make the silpoly a little shorter, like an inch or two?

I know silpoly isn’t supposed to stretch, but it must stretch some.  And I think the main thing, is it doesn’t stretch more after you erect it when it gets wet or changes temperature (compared to nylon).

Regarding silpoly, it’s a misconception that it “doesn’t stretch”. Comparing our 20D Silnylon and 20D Silpoly, for example, they have comparable stretch in warp/weft and on the bias.

As Jerry said, the big thing is that it doesn’t stretch or take on much moisture when wet or in high humidity. I’ve yet to make a mid, so I couldn’t comment on how that changes the design considerations.

Kyle B makes a good point- and I think it’s especially important that silpoly still has more stretch on the bias than it does warp/weft. I made a mid with 2″ of cat cut on the ridge lines (it’s a 9×9), I think the pitch would be more taut with a 3″ cut.

when you do a lot of cat cut deflection, like 3 inches, it really narrows up the peak area.  You lose a lot of headroom.

But, you can make it up by making the pole a couple inches longer

So it is sounding like a cat curve may still be desirable to ensure a taut pitch at the time of setup, thanks for all of the input.  Even though the silpoly won’t take on moisture throughout the night causing sag, a ‘mid design could still benefit from cat curves, regardless of fabric.

Of course there is the camp that doesn’t bother with curves on a ‘mid, and claim they wouldn’t use them if they sewed another one.

I did 2″ cut because I thought the poly would need less cut, and because I didn’t want to lose too much room inside.  There are a few little wrinkles when it’s tied out only at the bottom.  I think it would look more smooth with more cat cut, but. . . . . it’s really fine, and I think it will look better than a silnylon one after a rain or heavy dew, and I’m happy not to lose more room inside.

Thanks for that experieince

When the silpoly gets wet, can you just shake it off when you’re packing the tent?

When silnylon gets wet, I can shake it off but it still retains a bit of water.  Not a huge deal, but…

Final question before placing an order:  should I be subtracting 2″ from the height of the panels to account for stretch like in Jerry’s article with silnylon ‘mids?  Since the silpoly stretches as much as the silnylon while dry, so does this need to be taken into account while cutting fabric?

Sorry for all of the questions and polluting this thread.  I fully plan to start a new thread when I sew this thing.

That’s how I interpreted Kyle’s response, silpoly stretches the same as silnylon, but I wish someone would have more direct experience.

You can order, but when you cut it is when you have to make the decision.

I was thinking about cutting one without subtracting the 2 inches, very carefully measure, then stretch it (I’d have to sew on some grosgrain loops) and then measure and see how much it stretches.

Maybe someone could measure their tent, first when it’s not erected, then again when it’s set up.

Stretching Silnylon causes a certain amount of damage to the fabric at the stress points: Pole tops and stake loop areas. This is the primary reason I recommend a 10:1 (mineral spirits/100% silicone caulk) coating. Set it up very tight, then re-coat everything, leaving it to dry overnight. In fall weather, ie between 50-70F, use white gas because it evaporates quicker.

My son made this 9×9 from reading the archives here on MYOG/BPL. It took him a month of after school and weekends. That is now 3 years and 50-60 nights ago. No issues. It’s old school silnylon, and he did a cat curve, but not sure how much.

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Nice looking tent

I made my first pyramid when I was about 15.  It has led to degradation from there : )

I believe he mentioned you, Jerry, as the main guy to listen to.

@eric – yes I did end up making a 9×9 silpoly mid and took it to Norway for a couple weeks. I went with 2″ cat curve, and would have gone with 3″, as the panels were a little loose, no matter how hard I tensioned. What I ended up doing to deal with bias stretch along the edges was to pitch the corners low to the ground, and the middle of the panels a little above the ground. This seemed to help flatten out the panels, but was unacceptable in driving rain, as the raised middle of the panels allowed wind and elements in sometimes =[ I toyed with this idea for a fix to this problem:

https://backpackinglight.com/forums/topic/thoughts-on-orientation-of-woven-fabrics-relative-to-shelter-orientation/

And I also thought about shortening the length of the edges a bit, so that when the edge and middle seams stretched to the same tension the whole bottom of the mid would be on the same plane. Just an idea…

@ Jerry – I found the silpoly easy to shake off and put in the bag. The main problem didn’t seem to be with absorption of any sort, but just droplets sticking to the outside due to surface tension. Never any misting even after spending 20+ hours under driving Nordic rains thanks to the material, a huge vent and lots of wind, and lots and lots of fresh seam sealant  =]   The webbing was of course soaked though.

Pics of the finished mid:

https://backpackinglight.com/forums/topic/my-completed-mid-thanks-for-the-help-bpl/

Can’t wait for mid 2.0 !