Ultralight case for ND filters?

Are you referring to circular filters or the square/rectangle ones?

Hey Andrew, the circular ones.  The biggest one I have is 72mm

Here are some photos of a 0.7oz home-made filter holder for 87mm filters – would be lighter for 72mm. You could add a catch or tape to hold it closed, or put it in a zip lock as I did to keep closed and keep dust and water out. With the right sized taller lid or plastic bottle segment, you could fit two or three filters on top of each other with a similar DIY holder.

If your filters are of the same size, this could work :

called filter stack caps

I have aluminium filter stacks that I got of eBay but I haven’t checked the weight. I like the idea of using a jar lid but.

I ordered some filter stack caps, but they were heavy. Unfortunately, the weight specs are often not available or not very accurate online for many of these accessories.

The joys of buying on line…

Another just as compact but lighter solution could be two push on lens caps :

Thanks guys.  What kind of push on lens caps are those?

Im also considering making something out of reflectix…not sure how that will work yet.   I recently made reflectix lens protectors that came out pretty awesome.

Just generic push on caps, an alternative to the clip on types.

Ideally you would want to try them on your filters but they usually acomodate minor differences on filter/lens sleeve sizes.

They are sold by filter size (49/52/55mm…)

for example :

https://www.bhphotovideo.com/c/product/125291-REG/Kaiser_206958_58mm_Push_On_Lens_Cap.html