Hi stuuke,
It’s unlikely that all three polyfoam layers in the Butterwood Plush are 36 ILD (which is firm) but the ILD isn’t important to know anyway since you can feel the firmness of a mattress when you try it out and if all 3 layers are 1.8 lb density then they would meet the quality/durability guidelines here and there would be no lower quality materials or weak links in the mattress that could compromise the durability or useful life of the mattress for a child’s weight. My biggest concern given that the mattress has “plush” in the name is that it would be firm enough for a child.
Again the ILD isn’t important to know when you are testing a mattress locally but these are both high quality and durable materials so there are no weak links that would compromise the durability or useful life of this mattress.
Phoenix