Can You Microwave Fels Naphtha Soap?


Exactly two years ago today I wrote a post about how to microwave Ivory soap for your homemade laundry soap mixtures.  Putting the Ivory soap in the microwave made it puff up and once it cooled, it could easily be crumbled into a powdery consistency, saving you the time and energy of having to grate the soap.  I also made mention in that post that this would only work with Ivory soap – other soaps would just melt in the microwave.

how to microwave Ivory soap

Apparently I was kinda wrong about that.

Helpful readers have been chiming in and letting me know you can microwave your Fels Naptha soap too. Really??

Fels Naptha Bar Soap as you may already know, is made for laundry use and is a VERY popular ingredient in homemade laundry soap mixtures.  But of course adding Fels Naptha to your homemade mixtures usually means going through the tedious (and often tiring) step of having to grate up the bar of soap – and some of my clever readers have found a way to avoid that.

Bar of Fels Naptha Laundry Soap

What My Readers Had To Say

Here are some of the comments I received that got me thinking it might be time to test out putting my Fels Naptha in the microwave:

From Lisa:  

I microwaved Fels Naptha and crumbled it just fine. No problems at all. Mixed with the borax and washing soda…best laundry soap for us here! We have a small farm and it does the truck on every load! ( at a fraction of the cost)  Happy Mom here!

From Patti:

Me, too. I cut the Fels into 6-8 smaller pieces, put it on a large dinner plate and microwave it. It expands, it does NOT melt, and when it’s cool, I put it into a large Ziploc bag and crumble it with my hands from the outside of the bag. No processing needed!

From Lindsey:

Actually, you CAN microwave Fels Naptha bars just fine! I usually microwave mine for about 2-1/2 minutes. It grows a lot, though not nearly to the ivory soap scale, but stays together just fine. Note though that it seems to get hotter – you need to let it cool for longer than you do with ivory – but once cool can be broken up (it’s brittle) and thrown in a food processor. Works like a charm! I will also say that it has a stronger scent than the ivory, but I use this microwave method for either brand! =)

From RVance:

Microwaving the Fels Naptha really works!! I was able to crumble it with my hands and most of it fell into a powder. I had huge problems grating this soap, enough to say I would never do it again and then I saw the idea to microwave it. I was able to make a new batch of detergent in just a few minutes (after letting the soap cool).  Thank you!!!!!

OK, people – you’ve got me curious now – time to give it try!

How to microwave Fels Naptha Soap to make Homemade Powdered Laundry Soap

The Process:  How To Microwave Fels Naptha Soap

After reading some of these positive comments, I really had no doubt that it was possible to microwave Fels Naptha soap.  But just to be sure I gave it try, and it worked just like my readers said it would.

Here’s what I did:

I put my unwrapped bar of Fels Naptha soap on a dinner plate and cut it into six smaller pieces.

How to microwave Fels Naptha soap


I microwaved my Fels Naptha for 2 minutes total.  After the first minute it was just starting to puff up and looked like this:

How to microwave Fels Naptha soap


During the final minute it puffed up a lot more and ended up looking like this:

How to microwave Fels Naptha soap


I let the pieces set for 20 minutes to cool off, and then crumbled the pieces into my food processor and pulsed a few times to turn them into a final powdery consistency.

How to microwave Fels Naptha soap


Helpful Observations:  The Pros and Cons

So yes, the process does in fact work.  You can put your Fels Naptha in the microwave and it won’t melt.  It will instead puff up and once it cools down it can be crumbled, and then pounded or otherwise processed into tiny powdery pieces.

Before you give it a try however, here are a few more things to consider:

  • The Strong Smell

Fels Naptha bar soap has a distinctive fragrance.  I found that heating up Fels Naptha in the microwave really brought out that rather unique and strong smell.  I was happy I was doing this experiment in the warm weather so I could open my kitchen windows wide and let in some fresh air. My kitchen smelled like Fels Naptha for the next couple of hours.


  • Cooling Time vs. Grating Time

It will take about 15 to 20 minutes for the heated pieces to cool down.  On the day I was doing this experiment I had three bars of Fels Naptha that needed grating.  So during the cooling time for the first microwaved bar, I decided to grate up one of the other bars using my usual hand grater method.  It took me 15 minutes 🙂  So do you save time?  If you only have one bar to grate, then maybe not.  But if you have three bars, then I would say yes.  Three bars can be cooling down at the same time, but you can’t grate three bars at the same time.  {at least I haven’t figured that one out yet! }

How to microwave Fels Naptha soap


  • Good Final Consistency

What I liked best about this method was the final consistency of the soap flakes. Microwaving the soap seems to dry it out a bit too.  This makes it less sticky and more crumbly, and thus easier to get into a final powdery consistency that blends in nicely with the rest of the homemade laundry soap mixture.  Also if you don’t have a food processor, I tried the ziploc bag method too for crushing the microwaved pieces (suggested in the comment by Patti above) and it worked great.

How to microwave Fels Naptha soap


The final verdict?  This is definitely an alternative method that works. You can put Fels Naptha in the microwave and it won’t melt.  It might be kind of smelly, but it won’t melt.

If you’re willing to have the fragrance of Fels Naptha hanging around your kitchen for a while, then you can definitely save yourself the time and energy of grating and the end result will be fine powdery soap flakes that work well in homemade laundry soap mixtures.

Need a powdered homemade laundry soap recipe to try?  Here’s the link to the recipe that’s my current favorite:   Big Batch Powdered Laundry Soap Version 2 

Homemade Laundry Soap with Fels Naptha

How about you?  Have you been brave too and put your Fels Naptha in the microwave?

Feel free to share with a comment below 🙂



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  1. Hello
    Just for fyi😊 I put my felsnaptha in the microwave for 3 mins and it melted and started to burn😳can I still use it?
    Thank you

  2. I had some Fels Naptha that I had had a while. It was rather dry, so I just cut it in small pieces and put it in the food processor. It processed perfectly. It made a fine powder. I mixed a gallon and a half of powdered laundry soap during that time. I did this last year. I think I’d had the soap for a bout a year. The paper on the soap came unglued on the ends, so it did try out. Love this laundry soap.

  3. No, but i did grate up about a half cup of the stuff, put it on the stove in a corningware dish on HIGH for a few minutes. The smaller stuff melted, but the bigger chunks did not.
    I then took the bar that I grated, which incidentally looks pretty much like yours above, and put it in a little food processor we don’t use very much. My husband put some spice in there the other night trying to grind it up (I am not very fond of rosemary) so NOW I have some pieces of Rosemary in my processed Fels-Naptha. So NOW what do I do with the now-powdered bar?

  4. Microwaving obviously saves on a bit of time and the effort used in grating the Fels Naptha bars but . . .

    Does microwaving the Fels Naptha laundry soap bars change the chemical compounds in any way that may lessen its effectiveness?

    Is there a Chemist out there that could possibly answer this question?🙏🏻

  5. Will be trying this method soon, I usually make 3 or more batches at a time and the grating wears your hands out. This will be a God send ! Thanks.

  6. I love the microwave use of the bar soap!! Thanks for the tip, PLUS the smell is so CLEAN smelling. Way better than busting your knuckles with the grater. 😉

  7. I just microwaved Fels-Naptha for the first time! So, easy!! I will not be grating anymore, not even if I only need one bar!! LOL. Thanks for the pics. The pics were proof that it wasn’t going to melt and make a big mess to be cleaned up afterward. Oh, and I love the way Fels-Naptha smells, so that wasn’t a deterrent for me at all. Thank you so very much!!

  8. Just be sure not to burn it otherwise your microwave will smell like burned laundry soap every time you use it for months. Speaking from experience LOL

  9. I was lucky enough to find an older used microwave at a yard sale. The timer didn’t work, and it was on high all the time. I took it outside and cooked a bar of Zote soap right on the oven plate. The odor stayed with the microwave for a good while, but I am going to use it only for soap making. Made an excellent batch of laundry soap.

  10. Does anyone have any tricks as to how to get the smell out of your microwave I tried using vinegar but it didn’t work really well

  11. PAfter microwaving the Fels Naphtha and cooling it, like Patti, I put it in a large ZipLok bag and crumbled it by hand, then rolled it with a rolling pin until it was a nice powder. Didn’t take much more time and was worth it.

  12. Be careful doing this. We have an expensive convection microwave. I covered one bar with wax paper and immediately took the bar outside to cool. I cleaned the inside of the microwave, left the door open for six hours, cleaned it again…and three days later there is still a fragrant smell in the microwave. It is faint and does not impact the food, but I will not be doing this again for fear of ruining the microwave, which it surely would over repeated usage.

    1. I’m not sure if you can microwave a castile bar soap or not. I will have to add it to my list of things to try! My understanding is Ivory puffs up well in the microwave because it has air pumped into it in the manufacturing process. But now that I found out Fels Naptha puffs up too, I guess I’ll have to experiment with other soaps and see how they react too.

  13. I’ve done this a couple times and found that the soap somehow clung to my microwave. It was bad enough to make the food microwaved in it taste bad for a few months after using it this way. I decided to go get a cheap microwave from Goodwill for this and other non-food applications.

    1. Sorry to hear the smell was affecting your food. I had a little bit of smell linger, but not to that extent. A second hand, cheap microwave is a good solution if you can find one.

  14. HI Bev. Im looking forward to doing this, but wondered does this hurt the microwave any as per the soap smell? I know burnt popcorn lingers. All safe for putting food in microwave later or is everyone using an old microwave? Thanks!

    1. Good questions Sue – I just did this in my regular microwave and the smell lingered a little bit but not too bad or too long. I think I left the microwave door open for a while when I was done too and that helped. It was Ok to put food in the microwave afterwards too. Watch the soap and once it’s puffed up, don’t heat it any longer than necessary.

  15. I use the zip lock bag method as well. I crumble a few pieces at a time in a gallon bag and give it a few swipes with a rolling pin, works like a charm.

  16. I microwaved my fels on a paper plate and immediately covered it with a microwave splatter cover when I opened the door after ‘cooking’. This mitigates the odor – I also had the stove fan on high. Once covered, and with an oven mitt on, I flipped it over and took it outside to cool. If it is winter where you are (or at least cool out) this is a fast process – and crumbles easily.

  17. Just a quick thought – you do save time as you could be doing something else in that 15 minutes and let the microwave do the work on the Fels Naptha bars.

    1. If you don’t have a microwave you will have to stick with the traditional way and grate the Fels Naptha with a hand grater. Or watch for an old food processor at a thrift shop or a garage sale and keep that around for using only for grating your Fels Naptha soap.

  18. I just tried it and my plate cracked after a minute or so! It was microwave safe. I do not know why it happened, but folks might want to consider this when trying. Otherwise, I am looking forward to the results with no grating!

    1. Thanks for sharing that experience Caroline! That seems kind of strange that a microwave safe plate would crack.

  19. thanks for the idea….I gave up making my own bc I tore a tendon in my thumb grating Fels. I am going to try this.