What do you find best suits your filament storage needs?

[NeverDie]

I mentioned this one indirectly, but for your case I probably should have mentioned it directly. 20 gallon, IP68, full see-through, and half the price of the one you liked from home depot:

You may be right about the IP rating. I’ve given it a heavy weighting though because it’s the only proxy I have, whether good or bad, for trying to judge how tight the seal is. For a drybox, we want it as tight as possible. Why? I’m wagering the seal is where the bulk of the moisture intrusion is going to happen far more than the moisture intrusion through the plastic walls. Am I wrong? The only way to be completely sure would be to run some experiments, but short of that I don’t know where else to look for guidance on this issue. FWIW, the AI’s I’ve consulted think the seal is the likely weak point, but they aren’t always right, and I haven’t yet tried to double check their conclusion.

If anyone knows of a different way or a better way to judge it, please post!

[CarbonForge]

I just want to say this is a brilliant idea, I’ve been trying to come up with a solution to help my filament storage unit for awhile and this is exactly it. Thank you!

[Bratling]

You’ve prompted me to do so more research!

That Sterilite bin is likely one of the best choices – both bin and lid are made of polypropylene. PP is a moderately slow transmitter of water vapor, while polycarbonate (used in the lids of the Husky and Walmart bins) is a much higher (~20x).

Silicone’s performance is pretty awful, anywhere from 100x to 1000x the WVTR of polypropylene. It’s likely to be the main source of water vapor getting into the bin. Followed by a polycarbonate lid.

So: I would conclude that all these bins we’ve looked at are all going to be moderately-to-very good against liquid water ingress, but not so much against long term water vapor. I think I’ll be adding a big package of desiccant to my bin now, as it has a PC lid and silicone gasket!

I am beginning to understand why camera and medical dry cabinets are so expensive. And made of mainly metal & glass.

[NeverDie]

Good to know! Inspired by your post, I had Grok rank order different gasket materials by WVTR:

Rankings

Metal gaskets have the lowest WVTR (essentially zero through the material itself). Among common compressible gasket materials, PTFE (and especially PCTFE) and butyl rubber (IIR) perform best.

Why Metal Gaskets Win for Lowest WVTR

• Solid metals (e.g., stainless steel, copper, aluminum, soft iron) or metal-containing gaskets (spiral-wound with metal windings, ring-type joint/RTJ gaskets) do not allow molecular diffusion of water vapor.
• Any real-world “leakage” occurs only at the sealing interface (minimized by proper compression and surface finish), not permeation through the gasket body.
• Comparable to steel or glass in barrier performance (~0 g/m²/day). This is why they are used in critical high-pressure, vacuum, or hermetic applications.

Best Non-Metal Options (Ranked by WVTR Performance)

Here’s how common gasket materials compare for water vapor barrier performance (lower = better):

Rank	Gasket Material Type	Relative WVTR Performance	Key Notes / Best For	Limitations
1	Metal (spiral wound, RTJ, flat metal)	Lowest (≈ 0)	Critical seals, high pressure/temp, vacuum	Less compressible; needs good flange finish
2	PCTFE (e.g. Kel-F)	Extremely low	Precision seals, cryogenics, high-barrier needs	Stiffer, more expensive, less common for large gaskets
3	PTFE (solid or expanded)	Very low	Chemical resistance + good barrier; sheet gaskets, envelopes	Can cold-flow under load; lower compressibility than rubber
4	Butyl rubber (IIR)	Lowest among elastomers	Compressible seals needing moisture/gas barrier (vacuum, desiccated systems)	Moderate chemical/temp resistance vs. fluoroelastomers
5	Fluoroelastomers (Viton/FKM, FFKM)	Low–moderate	Chemical + heat resistance	Higher WVTR than butyl or PTFE in direct comparisons
6	EPDM	Moderate	Water/steam service	Higher WVTR than butyl
7	Nitrile (NBR)	Moderate	Oil/fuel resistance	Higher WVTR than butyl
8	Silicone	Highest among common rubbers	High-temp flexibility	Poor moisture barrier (“like a sieve” for water vapor)
-	Graphite / Flexible graphite	Low (when dense)	High-temp chemical service	Can be porous if not compressed well

Key data points:

• In direct ASTM E96 testing of same-thickness rubber sheets, butyl rubber showed the lowest WVTR (only ~1.24% of silicone rubber’s rate), followed closely by EPDM (~1.86% of silicone). Silicone was by far the worst.
• Butyl rubber is specifically specified (e.g., AMS7601) for low moisture and gas permeability in seals and desiccated systems.
• PTFE has very low water absorption and permeability (often 0.0045–0.30 range in normalized units); PCTFE is even better for moisture/gas barrier due to its chlorine substitution, though PTFE is far more common for gaskets.
• Silicone’s high polarity and Si–O bonds make it highly permeable to water vapor.

Practical Recommendations

• Absolute lowest WVTR — Use metal gaskets (or metal-reinforced composites).
• Best balance of low WVTR + compressibility + chemical resistance — PTFE (or PCTFE where available) sheet/ envelope gaskets.
• Best elastomeric option for moisture barrier — Butyl rubber gaskets (or halobutyl variants). Excellent for applications like vacuum seals, electronics enclosures, or where you need a soft, conformable seal without high permeation.
• Avoid silicone if moisture barrier is important — it excels in temperature range and flexibility but fails as a vapor barrier.

Other factors that matter:

• Thickness — Thicker material lowers WVTR (longer diffusion path).
• Compression & density — Better seating reduces interface leakage (more important than material permeation in many real gaskets).
• Temperature & humidity gradient — WVTR increases with temperature.
• Fillers & construction — Some fillers can increase or decrease permeability.

For your specific application (temperature, chemicals, pressure, compressibility needs), metal or PTFE will almost always give the lowest practical WVTR. Butyl rubber is the top choice when you need a traditional rubber-like gasket with excellent moisture resistance.

I guess if we had our druthers, butyl might be a better choice (1.24% the WVTR of silicone, according to Grok). That said, I’d take a good seal with silicone over a bad seal with some other material.

[Bullocks]

There’s gotta be some easy way to take a snake of standard 4mm od ptfe and join it suitably so it acts like a reasonable vapor gasket. We’ve all got it lying around lol. Maybe a tpu double ended plug, to join a circle. Hmm.

[Bratling]

@Bullocks

Maybe a tpu double ended plug, to join a circle. Hmm.

Had a similar thought, but TPU isn’t an effective material for blocking moisture. It’s the active material in Gore-Tex, used specifically because it allows water vapor to pass through easily.

You’d also want to kind of TPU you have. Polyester-based will degrade with exposure to water. Polyether will not, but is even more permeable. :-/

We’re heading deeper in the materials science rabbit hole here, aren’t we…

[NeverDie]

@Bratling

We’re heading deeper in the materials science rabbit hole here, aren’t we…

Yes, but that’s exactly what we need!

Google AI had some ideas about how to replace a silicone gasket with a viton gasket:

Summary

The easiest way to replace a silicone gasket with a Viton (FKM) gasket is by using Viton O-ring cord stock paired with a splicing kit. [1, 2]

Because Viton cannot be bought as a liquid squeeze-tube sealant like RTV silicone, you must use a solid elastomer. Instead of paying for an expensive custom-molded factory gasket, you can easily build your own to any size using the cord stock method. [3, 4, 5]

The Splicing Method

1. Buy Viton Cord Stock: Measure the width of your dry box’s gasket groove and buy a matching diameter of round Viton cord stock (or a profile shape like D-profile if your groove requires it). [2]
2. Measure and Cut: Lay the cord into the groove of the dry box to get the exact length. Use a splicing jig and a razor blade (often sold together in an O-Ring Splicing Kit) to make perfectly clean, 90-degree cuts on both ends. [1, 5, 6]
3. Glue the Ends: Apply a single drop of specialized cyanoacrylate (super glue) or rubber-toughened O-ring adhesive to one cut end. Hold the two ends firmly together in the jig’s alignment groove for 30 seconds. Once cured, the joint is chemically bonded and just as strong as the rest of the loop. [6, 7]
4. Press into Place: Push your newly made Viton ring directly into the dry box channel. [4]

Alternative “No-Glue” Easy Method

• Overlapped Cord Stock: If your dry box has a deep, tight channel groove, you don’t even have to glue the ends. Cut the Viton cord stock about 1/4-inch too long. Pack it tightly into the groove, and let the two ends smash directly against each other. The physical compression of closing the lid will force the ends together, blocking moisture without any adhesive.
• Pre-made AS568 O-Rings: If your dry box is a standard circular or square enclosure (like a pelican case or diving canister), check if the groove matches a standard American (AS568) size. You can buy pre-molded Viton O-rings online for a few dollars each. [7, 8]

The One Critical Catch: Latch Force

Before you swap them, check your dry box latches. Silicone is incredibly soft and squishy. Viton is a dense, tough industrial rubber (typically 75 Shore A durometer). It requires significantly more closing pressure to compress. If your dry box has flimsy plastic tabs or weak latches, they might snap or refuse to close against a solid Viton gasket. [1, 9, 10, 11]

If you want to make sure your box can handle it, tell me how thick the current silicone gasket is and what kind of latches the box uses (e.g., plastic snap clips, heavy-duty metal toggle latches, or thumbscrews).

[1] https://www.grainger.com

[2] https://www.grainger.com

[3] https://www.youtube.com

[4] https://www.youtube.com

[5] https://www.youtube.com

[6] https://www.globaloring.com

[7] https://www.theoringstore.com

[8] https://www.globaloring.com

[9] https://www.home-barista.com

[10] https://www.home-barista.com

[11] https://www.facebook.com

but it points out the clamps may not be good enough to get a good seal. I think maybe we’d be better off buying something (but what?) that’s engineered for the purpose we want rather than a retrofit. I don’t know. What do you think? What would it cost? The alternative is a lot of desiccant changes.

If money were no issue, I notice there are dry cabinets on amazon that allegedly maintain < 10%RH through self-regenerating desiccant. Expensive, but it’s large enough it could probably hold your entire filament collection:

320 liters would likely hold 80 or more 1kg rolls of filament. Just plug it in and you’re done. True set and forget. Or perhaps it uses a nitrogen generator to maintain dryness forever? I suppose that might be a different way to do it.

[krellboy]

They are kind of cheap compared to my other bins and I’m not sure they are strong enough to be stackable. If you are going to order some, order them in multiples of 4 and you’ll get them boxed.

Instead of desiccant in mine I use cheap calcium chloride “damp rid” type buckets. You just need to be careful not to slosh/drop them. They are about a buck and pull out cups of water.

[NeverDie]

@krellboy

Instead of desiccant in mine I use cheap calcium chloride “damp rid” type buckets.

What RH% are you getting with that? Perhaps I read wrong, but I had dismissed it because I had read it couldn’t drive RH% below 29% no matter what, whereas with enough well dried silica gel I can drive it down below 10%.

Of course, that’s not to say Silica Gel doesn’t have it’s own issues:

What color silca gel desiccant do you prefer?

By the way, with respect to maintaining a low relative humidity for keeping filament dry, Google AI had a clear explanation as to why it’s already too late by the time your color indicator becomes noticeable: Gemini Explanation TL;DR: If you rely solely on the color dye to tell you when to bake your beads, your high-purity nylon or PETG filament will already be actively absorbing ambient moisture from the air before the indicator tells you there is a problem.

[NeverDie]

Of possible interest, there seem to be both military and ASTM standards as it relates to humidity incursion:

Military-standard testing, including:

• MIL-STD-810E Method 507.3 Procedure I (Relative Humidity) — cycling high humidity (often ~95% RH) with temperature swings.
• Water-vapor transmission/permeability testing (ASTM E96, MIL-C-4150J, ASTM D 1008-64) on many models (especially Hardigg roto-molded cases).

though I just learned of this, so I can’t yet say how relevant they are or aren’t. It would make sense though that the military would have a longstanding active interest in “keeping its powder dry,” a phrase so common it was an OG meme.

One refinement which is alleged to have benefit is breathing desiccant valves, which allows air pressure inside a case to nearly equalize with outside air pressure by means of a valve that triggers whenever there’s enough of a pressure difference. When it triggers, the air first passes through a desiccant cartridge, so that it’s dry before it ever gets inside the case. It’s clear this is better than having the case breath on its own without any desiccant involved. It’s maybe less clear, but alleged to be better, than putting the breather desiccant inside the case. I can see an advantage though if you have both the breather desiccant and desiccant inside the case: you could then change the breather desiccant without having to open up the case, so maybe that confers at least some advantage. Is it significant? Maybe so, or else why would people bother with the added complexity? That’s a rather weak argument though, so I’d hope there’s more to it. Anyone know?

By the way, Pelican cases use silicon gaskets. Not EPDM or Viton. For such an expensive high-end case, I’m a bit surprised, but maybe Pelican’s clientele only care about easy-to-see stuff like water incursion far more than moisture incursion. Pelican cases have manual pressure equalizing valves that keep out water but not moisture. They’re not breathing desiccant valves.