Membrane SilPoly Tarp Question

[justicehaze]

I am about to place an order for some membrane silpoly to make a hex tarp and have heard different thing about putting cat cuts into it or not... Who here has had experience with this material and has some suggestions...

[WaffleBox]

They're not really necessary. Kyle (owner of RSBTR) made a tarp out of it with cat cuts and said that if he had it to do over again, he wouldn't bother with them.

[dudeman_atl]

I made a tarp from the silpoly and did slight cat cuts. What a pain!

But several months later, I very much enjoy having them.

[ksbcrocks]

I haven't used cat cuts with it and I don't regret it all. This stuff barely even stretches on the bias even. The coating really stiffens it up.

[hungh13]

I am debating about this as well, so why are people prefer cat cut over non cat cut? Is cat cut depends on the type of materials?

[duckyy]

Cat cuts help keep the material taut if it stretches a lot like nylon.

[Boston]

I am debating about this as well, so why are people prefer cat cut over non cat cut? Is cat cut depends on the type of materials?

Cat cut's provide tension through the center of the tarp, which can prevent sagging or flapping from external forces (note: this does NOT counteract nylons tendency to sag when wet). The less stretchy a material is, the less noticeable this will be, so tarps made from cuben, or heavier weight materials will have less of a noticeable problem. I have not made a poly tarp without cat cut's, so I can't exactly comment on how a tarp will pitch without them, but looking at pictures I can still see some tendency to sag a bit in the middle.

Polyester still stretches. Hell, dyneema stretches, technically, just not very much. Polyester doesn't stretch as much as nylon, however it's also not as strong. That's the trade off. I haven't heard of any poly tarp failures yet though. When you put a tarp together the perimeter of the tarp will be stronger, and stretch less under the same load, because of the hem (or binding, if you so choose). This creates a frame effect where the center of the tarp can stretch further than the perimeter under load (like from wind). By adding a cat cut, you put tension through the center of the tarp, which helps resist this stretching.

A couple notes about cat cuts: I think a lot of people put deeper cuts in tarps than are needed. I've experimented with tarps with 3-6" deep cuts (over 6-8ft) and found that I can get away with much shallower cuts then i generally see recommended. Right now I use 3" over 8ft. Shallower cuts are also MUCH easier to control when sewing.