Top tube bag - what foam or plastic for structure?

[Mikepemulis]

I'm planning on sewing a toptube bag, and I'm just wondering what you all recommend for a stiffer material to give the bag some structure.  I went to my local Michael's to look for something, but struck out.  Any recommendations? 

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[Parmick]

I have used HDPE from Tap Plastic for some of my items.  Not sure if it will work for you: https://www.tapplastics.com/product/plastics/cut_to_size_plastic/hdpe_m_m_opaque/258

[Mikepemulis]

I have used HDPE from Tap Plastic for some of my items.  Not sure if it will work for you: https://www.tapplastics.com/product/plastics/cut_to_size_plastic/hdpe_m_m_opaque/258

Thanks!  Will try. 

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[MCandler]

use the thin plastic or poly binders from Walmart or Staples. You may even have some around the house if you have kids...
https://www.walmart.com/ip/School-Smart-Lightweight-Poly-Binder-1-2-in-Red/118487176?wmlspartner=wlpa&selectedSellerId=1658&adid=22222222227000000000&wl0=&wl1=g&wl2=c&wl3=42423897272&wl4=pla-51320962143&wl5=9026798&wl6=&wl7=&wl8=&wl9=pla&wl10=113146138&wl11=online&wl12=118487176&veh=sem&gclid=CjwKCAiA1L_xBRA2EiwAgcLKA7_wIo14hz7NBHu379oYQzl6scAv8bivbRPdDBj8HFfkqbflFvnT0xoCKnsQAvD_BwE

[taprider]

use a crazy carpet.  Far more plastic for the buck (or loonie)
https://www.canadiantire.ca/en/pdp/classicturbo-carpet-48-in-0825201p.html

[Adam Alphabet]

HDPE.
If you plan on using a zipper and opening with one hand (while riding) a lot of other stuff is too thin/flimsy. The bag won't retain it's structure and can make unzipping a pain. My experience anyways.

[camnrtn]

So glad you asked this, I'm also about to try a gas tank for the first time.
I don't want to hijack this thread, but can anyone provide any advice about how to add the plastic inserts? I've heard that you add them last, after you've turned the bag right side out (presuming you've sewn it inside out). But to my mind you'd need a plastic sleeve that's accessible from outside of the bag, which seems a bit awkward/ugly/likely to slip around. How do folks manage this?
Thanks!

[taprider]

you could sew the fourth edge of each face closed after you insert the plastic
or you could leave the bottom inside fourth edge open of the two side faces, insert the plastic while the tank is inside out, then bend everything back to right side out

[camnrtn]

thanks for the advice taprider. Do you know any stitching techniques that will create a nice neat finish if I sew the fourth side closed while the bag is right side out?
Re the second bit of advice - have you found that you're able to turn the bag inside out even with the plastic stiffeners in place? I've sewn a good few things but not used stiffeners much.

[taprider]

any stitching technique that folds under or tapes the edges that can fray and the leaves the most worked over seam on the inside of the tank will work
also to fold right side out, start at one end of the open zipper face and start pulling up the floor from that end through the open zipper (if this is really hard, then your tank fabric is probably already stiff enough that it doesn't need extra plastic)

[Mikepemulis]

Thanks, everyone.  The bag worked out pretty great using some hdpe I found at a fabric store.  I like the idea of using cheap sled material, and will go that route if/when I make more.

 As people described above, I left the fourth edge unsewed until I right-sided the bag and then just sewed that edge by hand.  Worked pretty well.  I've just taken it around the neighborhood but seems very stable. 

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[taprider]

looks good, especially with the frame bags