Print from the bag

Print from the Bag

Update 2026-08-08:  My Basic Puck (is base for the spool holder) was a bit too wide for my design. So I took Prusa's original part and reduced the diameter to 50 mm. The modified stl is here downloadable.
Also I modified the "Inner ring" to be hexagon. This makes it a bit easier to hold it in place through the plastic of the bag while tightening the outer ring.

Why use a big, bulky, and expensive dry box when your storage bag will do?

I usually store all my filament spools in sealable plastic bags with a packet of silica gel inside. For more hygroscopic filaments, such as TPU and PETG, I used vacuum bags for a while. But after two or three uses they often start to leak. They are more expensive, and in my experience not really better than good, simple sealable bags.

In the past I also designed a proper dry box. It could be used for storage, and you could print directly from it. But it used quite a lot of filament, was rather bulky, and was not completely airtight. 

Prusa is also selling dry boxes. They look very nice and are well designed, but if I want to store around 30 spools of filament, that quickly becomes expensive and takes up a lot of space.

So I thought:

Why not print directly from the dry bag?

All you need are a few small parts that you can print yourself. The bags are cheap: I pay about $5 for 15 zip-lock bags of 5 litres, size approximately 30 × 32 cm.

The idea

The filament spool stays inside the bag together with a packet of silica gel. The bag is clamped around a printed spool-holder insert, and the whole thing can be placed on the standard Prusa spool holder.

A small filament feed-through with a short piece of PTFE tube lets the filament leave the bag cleanly.

Do not worry if the little “spout” moves around while the print head is moving. As long as the spool can rotate freely inside the bag, and the printer can pull the filament without too much resistance, everything works fine.

See the pictures for the setup.

Design challenges

The biggest challenge was space.

I wanted the system to fit on a Prusa Core One+, using the standard spool holder. The spool holder is about 47 mm wide The puck is approx 50 mm wide, and many filament spools have a centre hole of only about 50 mm diameter. That leaves very little room.

The length is also critical:

• the spool must rotate freely inside the bag,

• the bag itself  must be clamped securely,

• and the whole assembly must still fit on the standard Prusa spool holder.

The result is a compact system with tight tolerances.

Parts

The design consists of:

• a central cylinder / spool-holder insert,

• two inner flanges (hexagon),

• two outer clamping rings,

• a small filament feed-through, with ring to clamp to the bag and a nut to clamp the PTFE tube..

• a short piece of PTFE tube,

• optionally:  2 flexible sealing rings printed in TPU.

There are two types of the  rings:

1. Deeper square groove
   This the inner ring (Hexagon) here you can glue a seal printed with TPU for a better airtightness.

2. Rounded shallow groove
   This is the outer ring. The rounded grooves matches the profile of the seal

Printing

I printed the axis / spool-holder parts in PETG.

My settings:

• Material: PETG
  I used Purefil, a Swiss brand.

• Layer height: 0.2 mm

• No special supports required, depending on your slicer orientation.

You do need a well-tuned printer, because the tolerances are tight. The thread is especially critical. I recommend using a little grease or silicone oil before screwing on the rings for the first time.

Do not force the parts. Work them in carefully.

Assembly

First mount the central cylinder with the two inner flanges in the spool.

Tighten the inner rings close to the spool, but leave just enough clearance so the spool can rotate freely around the cylinder.

Then prepare the bag.

Cut a 5 cm hole through both the front and the back side of the bag. I used a compass cutter with a scalpel blade on one leg. This makes it easier to cut a clean round hole.

Also cut or punch a 1 cm hole near the bottom of the bag, slightly off-centre. This is for the filament feed-through.

Mount the feed-through through the 1 cm hole and insert a short piece of PTFE tubing. Push the PTFE tube about 5–10 cm through the feed-through.

Now carefully guide the filament from the spool, from the inside of the bag to the outside, through the PTFE tube. Try not to let the spool unwind too much while doing this.

Place the spool inside the bag and mount the outer flanges to clamp the plastic of the bag between the rings.

Make sure the inner flange does not rotate while tightening the outer ring. Otherwise it may create friction against the spool.

Add a fresh or recycled packet of silica gel, close the zip-lock bag, and you are ready to print.
Add a little note when you put in or replaced the silicagel. So you can renew them in time.

Important tip

When you hang the bag on the printer, make sure the silica gel packet is at the lowest point of the bag in the printing position.

That way it stays out of the way of the rotating spool and does not interfere with the filament.

Why I like this solution

This design is:

• cheap,

• compact,

• easy to print,

• easy to store,

• and much less bulky than a dedicated dry box for every spool.

It is especially useful if you have many spools and do not want to buy or print a large number of dry boxes.

For me, this is a practical middle ground: better than leaving filament exposed, much cheaper than buying many dry boxes, and small enough to use directly on the printer.

Tip

Over time the silica gel will loose is capacity.
When you have an "active, heated" dry box, I have a Sokol box, then you can put in the whole bag inclusive spool, open the zip-loc, and dry it actively there at 40 - 50 C for 6-12 hours.  
I also then put in some fresh silica gel packs.
The old packs I recycle in a normal oven at 110 C for 2-3 hours.

Have fun!

As always:

If you like my design, please give it a heart.
If you print it, please share your experience and add some pictures.
And if you have questions, just ask.

PS Update

 I have made some small tweaks to increase performance. Just reload the files here.