Best combo poly/latex for a 4" thick cushion/mattress to be used full time on a boat- no memory foam

I’m looking for recommendations on what combo to use for 4" thick cushions, TIGHTLY covered in Sunbrella material that will be used on a boat full time for mostly sitting, but also convertable to sleeping.

I know there are many bad reviews of FBM but wow are they cheap. Some people seem to have an ok time with them however. Regardless what I end up doing the foam needs to be the highest quality and long lasting.

Here’s what I’m thinking top to bottom, queen size 60 x80

1" 20 ILD Latex topper from FBM
3" 38 ILD HD-36 HQ Polyurethane foam sheet.

(What should a queen size 3" HD-36 HQ weigh so I can make sure they sent the right quality?) Would it be wise to use Dacron batten on top of the latex or would that defeat the purpose?

From reading online I know the HD-36 HQ can be pretty firm, but I’m thinking if I cut it to 3" it will soften up a little. I also know the 1" Latex won’t matter much for sitting, but when laying down it may make the area a little softer and cooler as we live and will be in HOT locations! I am however afraid the above arrangement will be too soft for sitting.

NO memory foam and we can’t go more than 4 inches as thats what our covers will hold. I’ve had it before and it’s HOT! We are both side sleepers pretty much, my husband is 230 lbs and i’m 130 lbs. He likes a softer sleep to a firmer sleep. We currently have 4" foam that seems high quality and keeps its shape but bottoms out when you sit on it. I am also open to modifying this foam if you think 1" or 2" of a different foam in combo with our older foam would help.

Any suggestions on what the best combo would be?
At first I was considering 4" of the HD-36HQ, but figured 1" of the latex on top would make it better to sleep on. I don’t want the are to be too soft since its primarily a sitting area.

I was also thinking maybe 1" of the Lux-HQ, 2" of the HD36-HQ and 1" of the Latex 20ild, but Im scared this will be too firm.

If you have another 4" combo suggestion from a different supplier then FBM please list them.

Thanks so much from a very confused boat girl.

Hi Danibug,

As you probably know … I don’t recommend FBM for any purchase where getting what you think you’ve ordered is important or “application critical”. I don’t believe they even have any 20 ILD latex. You can read more or my thoughts about them in post #2 here and post #2 here. “Cheap” and good value are not the same thing IMO. Lots of things are cheap but there are not nearly as many that are good value.

Your design seems to be very firm to me and while it may be good for sitting … I would think it would be very firm for sleeping.

If you multiply the height x width x thickness in inches and then divide by 1728 you will have the cubic feet. multiply that by the density in lbs and you will have what it should weigh. I would also bear in mind that there are many cheap filled foams that have a higher filled density (vs the unfilled polymer density that determines the quality of the foam) but are still conventional foam and not the higher performing HR foam. If there is too much filler it will reduce the durability of the foam.

The dacron batting would be a matter of personal preference but it may add a touch of softness or “hand feel” to what would otherwise be a very firm mattress and it can help a material keep its shape with stretching. An inch of latex is not really significant and most of what you feel from this mattress would be the polyfoam. I personally would tend to use either a single layer of HR polyfoam (that really was HR) or a single layer of latex.

Thinner layers are actually firmer rather than softer because they compress to their maximum and bottom out much more easily. I believe this is the same “rationale” that FBM uses when they “rate” their softer latex and it certainly isn’t what happens with thinner layers. I would strongly suggest talking with a professional foam supplier that can give you much better advise for your specific application than FBM.

I don’t think it will be too soft for sitting (although the lower quality foam will have a lower compression modulus which may make a difference and it may bottom out more easily unless it really is HR foam). My concern would be more that it would be too firm for sleeping.

I will leave the specific design and layering to your discussions with your supplier because of the variables involved and they will be more knowledgeable about the specifics of the foams they supply but I would suggest that HR polyfoam or Dunlop latex … both of which have a much higher compression modulus (which is more important than ILD in your application and in furniture seating as well) … would be more suitable. I would choose a single layer of either if I was in your shoes.

Again though … I would not deal with FBM and I certainly wouldn’t speculate about what layering to use with their products when you have no real assurance that what they advertise is even what they sell.

This article along with this article and this article (all of which talk about polyurethane, support factor, and various other specs in terms of furniture design) may be helpful as well.


Thanks for the quick response. I have talked it over with my husband and we have decided to not order FBM. It’s too risky with all the commenters out there who have had bad experiences.

So I’ve been talking extensively with SLAB (Sleep like Bear) for a few days now and just yesterday decided to jump on a Scrap piece of 1" 21 ILD Celsion Latex topper. It’s a twin size and will work well with one area in the boat. My idea is to make a custom cover out of it and lay it on top of the current 4" Poly foam we have (I think it’s about 2.5/lb Density and 35 ILD). Do you think laying the 1" 21ILD Celsion Latex on 4" of 35 HD Poly will make a big difference in the comfort?

I believe my issue with the comfort is that the current cushions are too hard. When I sleep my arms and hips fall alseep. I’m assuming that’s because the foam underneath doesnt have enough give? We also sit on these cushions and the Poly 4" compresses quite a bit to about 1" from the plywood it lays on. Will the 1" 21 ILD Celsion on top make any difference when sitting on the Poly 4"? If you had to pick a 1" of an ILD for sitting ontop of 4" 35 ILD would your go higher to say 27 or lower to 15?

So now onto the Vberth (sleeping only area). We also have 4" of 35 ILD high density Poly foam that makes my arms and hips fall alseep. We are hoping to find a Celsion Latex ILD topper that will help this significantly, however we only have 4"-5" to work with. We are thinking of cutting 1" off of the Poly 35ILD foam and replacing it with 2" of the 21 ILD Celsion topper. This will then go into a TIGHT sunbrella cushion cover. That will be 5" total (2" 21 ILD Celsion over 3" 35 ILD HD Poly)

Do you think the 2" of the 21 ILD Celsion on top of 3" of HD 35 ILD will be soft enough so my arms and hips don’t fall asleep? I was thinking the TIGHT COVER over the Poly and Latex topper might actually make the 2" 21 ILD Latex seem too firm. Maybe in this situation we need 2" of the 15 ILD Celsion instead over the 3" of Poly? My husband is 230lbs and likes a soft sleep.

We are choosing the Celsion because we plan to cruise the tropics for many years with no AC. We need the foam to be as cool as possible.

Thanks so much. Also any other recomendations? :cheer:

**I thought I should add.

I know you said Phoenix, that you would either do full Poly or Latex in your above response, but since we already have Poly I’m trying avoid the cost and work of redoing it. I think it high quality, I suppose I just thought it was no good because my body parts were falling alseep. With the savings also we can afford the best quality Latex topper to put on top of our existing Poly Foam.

Hi Daniburg,

If you already have good quality polyfoam (other than from FBM which I have strong suspicions is not HR polyfoam at all which I think would be much better in your application) then adding an inch of latex would not be an issue of course. My thoughts are that an inch of latex on top of foam that seems to be too firm already and doesn’t have the range from softness to firmness (or what is called “ride”) may not make much difference anyway … at least for sleeping. If you only have 4" to work with then the support factor (also called compression modulus) of the foam along with the surface softness (ILD or IFD) with initial compression will be the most important specs and the biggest part of how well it works for the dual use you are considering. Support factor is much more important than ILD alone which appears to be too firm based on your “symptoms”. If I was to use both materials for your application i would probably consider 2" of each.



The foam we currently have isn’t from FBM and has held up over the past 6 years just fine with light use. If I add the 2" topper to 3" of the poly, won’t the latex be alot firmer and hotter in the TIGHT sunbrella cover? I’m toying with the idea of leaving the cushions poly 4" with the sunbrella cover and adding the 2" latex on top, but I need to cover it with something.

Do you think the latex will sleep cooler and be truer to it’s rated ILD number if it’s on top of the tightly cover poly or make no difference?

I worry shoving the 2" into the covers as is…a very tight fit…will make the latex sleep hot, be too firm and defeat the whole purpose of latex (especially the Celsion).

What kind of cover do you recommend? I can sew it out of any fabric and will have to since the cushions are odd shaped. I would prefer a Polyester blend mostly to avoid the mold and mildew issues that happen with cotton.

What ILD would be best you think for 2" of the Celsion Latex on top of the HD Poly about 35 ILD? 15, 21, or 27 ILD?

Hi Danibug,

If the foam you have is HR rather than conventional HD then this would be a good thing.

There are two separate influences involved when you are layering materials inside a cover. the first is that if you add a layer of foam to another layer on a firm surface … the two layers together will tend to be softer overall than either one by itself. This is different from the “feel” which will depend on which layer is on top and which is softer than the other.

If you put these same two layers inside a tight woven cover like Sunbrella (as opposed to a stretch knit cover) then the more the cover compresses or “squishes” the foam inside it the firmer the two layers will be compared to the same two layers that are not compressed. All foam gets firmer with deeper compression so how compressed it is is a big part of how firm it will feel. This is why compression modulus (support factor) plays such a big role in how firm a foam feels. If the Sunbrella cover only has room for the polyfoam and you try to “squish” the latex inside this will firm it up considerably. If you put the latex on top of the existing cover … then it will definitely need a cover of its own because latex will degrade much more quickly with exposure to air and light.

Don’t forget that ILD is only a rating at a certain percentage of compression of a foam and different compressions will have different ILD’s and an ILD measurement that is taken at 25% compression (which is standard) will change depending on the thickness of the foam that is being tested (25% is different with different thicknesses). The “standard” thickness that is used to test the IFD of polyfoam is 4" and the standard thickness used to test latex is 6" so the two are not directly comparable to each other.

Which of the two “influences” are dominant (the softening that comes from thicker layers or the firming that comes from compression) will depend on how tightly they are compressed inside the cover. Either way though … the two layers together will decrease the likelihood of “bottoming out” and allowing the feel of the firm surface below ti to come through. Even if it is compressed inside the cover, the starting … ILD will be firmer and it will get progressively firmer yet but will be much less likely to bottom out (reach maximum compression).

While latex has a more open cell structure than most other types of foam (and Talalay is more open than Dunlop) … compressing it will reduce breathability yes. The ventilation and ability of a fabric to wick or store moisture away from the body can also play a significant role in temperature regulation. This is why in general natural fibers (like cotton or wool) or semi synthetic viscose fibers (like bamboo or eucalyptus) are cooler than most synthetic fibers which don’t absorb moisture although some of them can wick it away fairly effectively.

It will perform more like a “typical” layer of foam of a certain thickness and of a specific 25% ILD would perform if it was on top of the cover rather than compressed inside it.

I would probably tend to avoid compressing the foam too much as well. While it will affect ventilation (which is the primary reason that combinations of materials are cooler or warmer) … it won’t affect the phase change gel in the Celsion which is a secondary cooling technology and compression would have little effect on this. The ventilation and ability to wick away and store moisture away from the body of all the layers combined (foams, cover, any protector or mattress pad, sheets, and blankets) will all have a combined effect which together determine the temperature regulation of the mattress. One layer that is not breathable can minimize or negate the ventilation effect of the layers below it although they won’t negate the effect of any thermally conductive or phase change materials below them.

This would probably depend on the overall design goals and the primary use of the system. Stretch knits would affect the softness and feel of the foam less than tighter and less stretchy weaves and in general synthetic will be warmer than natural or semi-synthetic viscose fibers like rayon which may make a good choice.

I’ve never slept on something like what you are building so I really don’t know but since Celsion (now called Talalay GL fast response) only comes in the 3 ILD’s you are mentioning … 15 would be way too soft, 21 would probably be too soft for sitting, so I would probably go with 27 which would have less risk of bottoming out on such a thin mattress.