Sounds like a quality issue. I bought a memory foam mattress from Costco a number of years ago and had the same thing. Returned it.

My parents have a split king mattress from Tempur-pedic and the two pieces are identical, for what that's worth.

I agree, 1929. Novaform mattresses are good quality, in my experience. I had one for 6 years, my sister has one, DD has 2. All are kings or queens. All have performed well. I don’t know if getting twin beds to match is an industry issue or an issue limited to this manufacturer. It is driving me nuts. I don’t deal well with lack of symmetry.

Thanks, F2BH. Good to know.

I'd say soldier on --- you don't want your MBR to spark the-opposite-of-joy. Ask me about a door knob that's been annoying me for a decade.

We have tempurpedic split king adjustable and they are exactly alike. It would drive me crazy if they were not. I have always heard good things about the Costco mattresses, though, so I would definitely keep trying to get two that matched, at least one more time. Terrible to have to go through this though.

In looking for a new mattress last year, I just cannot do foam - memory foam anyway. I don't know anything about the expanding process. Does that mean they come in a box and then have to fill to full size? I would keep going I guess because I sure wouldn't settle for two mis-matched mattresses. Well, like Outside said - give it one more try and if you still have problems, I'd be looking elsewhere. I have seen a king split mattress that splits only down so far - it was one piece, not two twins. But of course then you couldn't adjust the feet area (which we don't anyway - only the head). I have no experience with that type mattress, have just seen them.

Not a foam mattress, but years ago a friend’s husband wanted to replace his twin half of their king. She said she didn’t feel the need to change her half at that time. The problem was his new one was a pillow top or something and he was inches above her. 😆 So she decided to also get a new, matching mattress.

The mattresses I have are gel memory foam, just like my old mattress. I love it. It does not sleep hot. DD and DSIL have a Tempurpedic. I’m not sure if it has gel or not. DD hates it. She says it sleeps hot. A condo we rented had a foam mattress that slept hot. I cannot deal with that at all.

While painting and setting up the new MBR bed, DH and I have been sleeping in the guest room. We have Twin XLs in there that he hates - the size not the mattresses. I pushed the two beds together and made them up as one bed. Even with two mattresses, movement transfers from one mattress to the other. I really need a foam mattress for that if no other reason.

I’ll call Novaform again tomorrow to see what they have to say, but I’m going to spend some time looking at new mattresses today.

I bought costco's latex foam mattresses and they do not have to expand. they are perfectly symmetrical as far as I can tell and I love them!

https://www.costco.com/sleep-science-12%22-iflip-natural-latex-mattress-and-q-plus-series-adjustable-base.product.100431240.html

Bb the foam mattresses we tried were marshmallows. Not enough support and I felt like I sank into the marshmallow. Lol. We like a firm mattress. Ours is good re: transfer movement. I actually think ours has some foam around/over the coils. I’m glad we finally got one last year, I’d hate to be mattress shopping during covid.

Here’s the resolution, albeit maybe temporary. DH and I took each of the 4 mattresses and made pairs until we found a pair that was acceptable (if these weren’t twins, we would never have been able to manhandle them). We are going to sleep on them for a while and see how it goes. If it weren’t for Costco’s excellent return policy, I would not even consider giving it a try. Quite frankly, with the corona cooties making a new surge, I‘m tired of having people in my house which would happen if they were to send more new mattresses.

Tina, as I was putting the coverlet on, I remembered I had not put the Gorilla Grips between the mattresses and the base. I’m so worn out from wrestling mattresses, the Gorilla Grips will have to wait until I change the sheets...that is unless the mattresses start falling off the bed. 😆

Well, Tina, being slightly OCD, I made sure the center crease in the top sheet was between the two mattresses when I made the bed yesterday. Because of that, when I made it up today, I could tell the mattresses had shifted. I may have to get those Gorilla Grips out sooner than I planned!

I recently bought two twin XLs from Tuft and Needle and they're identical (and yes, they were the kind that arrive rolled up and expand). TBH, it seems really janky that a company would have such poor quality control with sizing.

I would suggest getting a compatible frame with a headboard and footboard, which that might mask the disparate lengths pretty well. the bar at the ends will push the mattresses up, so you could just put lots of big pillows at the head where it's uneven.

Regardless of the glitches with sizes, the mattresses must sleep well. DH and I slept 12 hours last night. I can’t remember the last time I slept 12 hours straight.