I have a water-filled punching bag that I can't use with sand (various reasons, but mainly rodents, this bag also can only be filled with water). It's 55L when full.

I'm looking for ways to prevent it from freezing during the winter while still using it. The lowest temperature registered in Vancouver, Canada is -17 celsius, so I'm looking for some anti-freeze liquid that won't cost a fortune, that I can keep in the bag many years (so summer + winter) and that doesn't corrode vinyl, which is the inner material of the punching bag.

What are my options? What anti-freeze liquids are safe for Vinyl? Would salt be safe? Given the price of some options, I would be ok replacing the punching bag every X years (e.g. every 5)

What I found so far is (all prices are canadian dollars):

Star brite Bio-Safe Non-Toxic PG All Year Anti-Freeze

This gives -20 degrees celsius protection. I don't know if this is safe for Vinyl or if it will last many years: http://www.starbrite.com/item/bio-safe-non-toxic-pg-all-year-anti-freeze-coolant-full-strength

Windshield Washer Fluid

This is what was recommended to me by the company producing the punching bag. I found this: https://www.napacanada.com/en/p/RCE49304W# I don't know how much I should dilute it (what percentage of water) and I'm also terrified of filling it myself: I need to use mask, gloves and eye protection (all stuff I don't have) and I have no idea of how to dispose or where to store the excess. I would leave it outside but I'm afraid of damage it could cause to the property or to the sewers if I disposed through that. I would be happy to pay someone for the work, but I don't even know what kind of store would do such a thing.

Winter Washer Fluid - different brand

https://www.amazon.ca/nextzett-94252015-Anti-Frost-Windshield-Concentrate/dp/B004PGS368/ref=sr_1_1?dchild=1&keywords=Winter+Windshield+Washer+Fluid+Concentrate&qid=1635655664&sr=8-1#productDetails I also noticed it's made of ethanol. Could I just buy ethanol instead? The company said not to use alcohol because after a certain time it will eat the vinyl.

  • FYI, it sounds like (based on the safety sheet) that the dangerous fluid contains methanol, and the fluid itself is methanol and isopropyl alcohol based. And you’re right that the stuff shouldn’t get into the sewers; the proper disposal is at a specific facility or apparently incinerated. The listing on that store also says the stuff is intended for industrial use. Idk what the people suggesting that to you were thinking, to be honest.
    – fyrepenguin
    Oct 31, 2021 at 10:07
  • 1
    most of the time it doesn't actually freeze in Vancouver, or barely, and then again at most maybe 1 or 2 weeks in the year. I would consider just moving the bag indoor when a cold snap is announced.
    – njzk2
    Oct 31, 2021 at 11:08
  • What is a better Stack Exchange site for this question? Punch bags do not really fit 'the great outdoors'.
    – Willeke
    Oct 31, 2021 at 12:01
  • I was thinking in the direction of Chemistry (but it might be off topic there as well.)
    – Willeke
    Oct 31, 2021 at 19:06
  • I did post in Chemistry and got some very good responses! Nov 6, 2021 at 6:54

3 Answers 3


The Star-Brite fluid contains propylene glycol, this is a common additive in foods and is classified as GRAS (generally recognised as safe) by the FDA, at the levels it is used for in food. I don't know about the safety of the concentrations in the product you linked, but it is generally thought to be fairly safe for both you and the environment. Check out the safety data sheet (SDS) at the page you linked, it goes into the safety aspects of it.

I looked up the effects of propylene glycol on poly-vinyl chloride (the most likely material for your bag) and came across this site, which is mostly about engineering - so pipes etc, and states:

Propylene Glycol C1-Fair

Meaning that it is not great for extended use in your bag, as it can leach plasticizers and cause structural weakness. I suspect it would be fine for a year or two, but I can't say for sure.

The second product, as mentioned in the comments, is mostly composed of methanol and isopropyl alcohol (IPA; check out the SDS on your linked page, linked as MSDS (for material SDS)). Visiting the same site, I couldn't see IPA on the page, but methanol is there as Methyl alcohol (10%) and states:

Methyl Alcohol 10% A1-Excellent

However, note the 10%... the product has 80-100% according to the MSDS. If you hover over the label in your linked page, you can see some tiny writing below the words "windshield washer concentrate" that states:

Directions: A mixture of 45% concentrate to 55% water protects to -37 C. 50% concentrate to 50% water protects to -40 C.

So at best you will have about 35% methanol, which isn't on the compatibility chart I found. However, given that ethanol and butanol (methanol = 1 carbon, ethanol = 2 carbon, IPA = 3 carbon, butanol = 4 carbon) both have a C1-Fair classification, I think it is probably safe to assume that methanol and IPA will both be problematic long-term. I don't know why the company recommends this product, but if they say it works, it would pay to contact them and enquire about how long-term etc.

As per comment from @fyrepenguin: Methanol is toxic to you and to the environment. It evaporates readily and can be absorbed through the skin, the lungs and via ingestion. If you go down this route, you definitely should make sure that you fill it outside, wear gloves, safety glasses and breathing protection. As it could well affect structural integrity of the bag, filling one with this, then subjecting to repeated impacts is possibly not a good idea .

The last linked product, according to Amazon contains ammonia - this is the stuff you might use to clean your toilet or clear drains. It stinks to high heaven and you should definitely take a lot of care during filling your bag. Do it outside and wear gloves, eye protection, long sleeves etc. It is apparently chemically compatible with PVC:

Ammonia, anhydrous A2-Excellent

Ammonia, liquid A1-Excellent

  • Based on some info I found, ethanol at 30% would be safe on vinyl and provide -20°C, which is enough for my usecase. I am reluctant with all the products because they are mix of things and are not for my specific usage, so something pure seems like a better fit. The company already said that filling with anything but water invalidates the warranty, but that's fine, I used it for the entire summer and the warranty is only 1 year anyway
    – Francesco Belladonna
    Oct 31, 2021 at 23:08
  • I think it would be important to add to this answer the fact that methanol is seriously hazardous to humans and the environment, and as such, if you’re planning on … punching a bag full of it, and are not certain how well it’ll hold structural integrity, that it would probably be a bad idea, as dermal exposure can be dangerous as well.
    – fyrepenguin
    Nov 1, 2021 at 7:02
  • 1
    @fyrepenguin - good point, I'll edit that in.
    – bob1
    Nov 1, 2021 at 7:30

A bit of a frame challenge: Don't protect against record lows, protect against typical low temperatures.

Vancouver has a similar climate to where I live. Our record low is -14.4°C. The lowest I've recorded at home is -13°C outside the city in a village, once in 15 years. The bag will probably never see less than -10°C, which means a lower concentration of antifreeze is needed.

It will actually take quite some time for that much water to freeze because of the thermal mass (heat capacity) of 55l of water, so an overnight temperature just dipping below what your antifreeze can handle wouldn't be an issue. Freezing will be quicker if the bag is black because it radiates heat into a clear sky. If it's under any kind of roof (e.g. hanging under a balcony) that will help with radiative heat loss.

I'd actually mix antifreeze for around -6°C, and if a prolonged cold spell was forecast I'd remove some water to allow expansion, possibly topping up the antifreeze at the same time. Covering the bag over clear cold nights with insulation of some sort would be a good idea, as is done with gardens plants at the limits of their range. Horticultural fleece would actually do quite nicely, or even just bubble wrap.

Then I'd probably go for propylene glycol at about 20%. Even with food grade PG this looks like about CDN$60--110 (converting from what I'd pay). Note that you're aiming for 20% PG, not 20% PG-based antifreeze.

Isopropanol would be my second choice, again at about 20% (or ethanol, but note that this would be in the form of denatured alcohol that includes some isopropanol or methanol, as well as other things that might not be so good for the vinyl)

Ethylene glycol is another possibility; it's common in car antifreeze. But it's toxic and attractive to animals so I'd avoid it in case of spillage and disposal.

  • Bring it indoors when not in use?
  • However, antifreeze is added to water, it prevents the water molecules from forming crystaline ice. So, antifreeze stops water from freezing until the temperature drops well below 0°C. However you must fill the bag half way which is probably expensive.
  • Failing that, An insulation layer that staves off chill longer. Boil a pot of water and top off the bag before hand.
  • It's 60kgs and (dangerously) filled with water, so I have to pass on bringing it inside, I have a lot of electronics at home and it will probably break my back over time. The insulation is also an enormous amount of work, it would be an every-day thing for couple of months, I'd rather spend the money one-off and be free. Nov 6, 2021 at 6:53
  • - What if you wrap it in an electric blanket. - Also if you pu the bag on wheels you can wheel it in
    – LazyReader
    Nov 8, 2021 at 5:24
  • won't the electric blanket break outside with rain? Nov 10, 2021 at 19:13

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