Prius Seat Mod 2.0 (Gen 3 Prius seat upholstery DIY)

Hey all, I have a 2010 Prius base and the seats were killing my back. Ealier I made a seat mod DIY on Priuschat titled:
The ultimate seat mod DIY for adding adjustable lumbar support on a Prius or any other car seat
where I show how easy it is to remove the seat and its cover to add extra padding. In my case, I added a hand pump operated air bladder to adjust the lumbar support. In that DIY, I also discussed possible variations you can make to improve the mod. This current DIY is meant to be a continuation of that post where I have implemented those variations.

After testing the earlier setup for awhile, I was not completely satisfied because the air in the bag kept shifting side to side and created uncomfortable creases. It also didn't solve the root of the problem which was that the OEM seat back support rods pictured below were jabbing into my back and the OEM foam padding wasn't thick enough to insulate the driver from this. Perhaps the foam has flattened to the point where it lost its padding. Or perhaps this is the abysmal level of interior appointments Toyota is willing to accept in order to cut costs (note the seat back foam is not very thick at all - only about 1/2 inch is my estimation, and the white plastic lumbar flap is too small as well, and its edges were stabbing into my back):


So the solution discussed previously was: insert a flex-board between the rods and the foam and replace the air-bladder with strategically placed layers of foam padding throughout the seat.

Materials you'll need for this diy:
-A 24" x 24" laminate board, 1/8" thick
-1/2" thick foam pad from Amazon (high density foam - not memory foam)
-3 extra small zip ties
-5 medium sized releasable zip ties
-optional: a 1/2" thick memory foam pad measuring 12" x 16"

First, you need to remove the seat and peel up the seat cover. My previous DIY details how to do this.

I realized that a laminate board is the most logical and available flex plate to use. It's made from mostly laminate glue so it's quite rigid and strong enough for this application while being flexible enough to conform to the oval shape of the rods (the back arch):


Here is how it looks after I cut and inserted the board. I forgot what the cut measurements were, but if you're doing this, you just need to measure it to fit inside the seat frame and it doesn't have to be exact. You just have to make sure it covers the entire back.


To insert the board, you need to realize that the rods are just held by an open white plastic ring bracket shown:


And they come out if you pull down as shown:


There is also a cable you need to detach with a 10mm socket before you can insert the board:


And just insert the board like this:


Now for the revised padding, I decided to take off the 3 hog rings attaching the top portion of the seat cover:



Now you can pull the cover up all the way to the top. Notice how at the factory they cauterized the left shoulder portion of the seat foam to harden it and patched it so it wouldn't wear out easily. I am not the least bit impressed by the level of engineering involved in this especially when it's done by the original manufacturer. Even though the Prius is an important model in the Toyota line of products, this is the kind of cheapo quality you can expect for the non-mechanical components when buying a Prius:


I then cut the foam sheet to size:



Then I traced the shape of the seat back with a marker:


After very careful tracing, measuring and cutting, I ended up with this piece:


I then traced and cut the 4 sectional borders of the seat created by the upper back, lower back and 2 side bolsters. Doing this will allow the seat cover joints and tension ropes to sink into the gaps and create a flush seating surface. Note: you cannot underestimate the level of precision and care required for this step as you only get one chance for a proper cut. For this reason I decided to remove the seat and bring it into my room as I have done before:



I then added a piece of memory foam pad from the previous mod cut to shape to give a bit of extra padding for the lumbar region. (Inserted underneath the hight density foam):


Now you want to pull the seat cover back down. But to do so, you must thread the seat tension ropes back throught their sleeves:


At this point, you can just hold the foam pices firmly in their correct places with one hand and start pulling the cover down. Midway down, you can replace the 3 hog rings with 3 small zip ties (I skipped this step because I didn't have any small zip ties and it didn't make any impact on comfort, but I am planning inserting them later as I used releasable zip ties for the main seat flap securements). After carefully threading the tension ropes through the cover and pulling the cover all the way down, you're almost done:


Now all that is left is to re-fasten the seat cover using releasable zip ties and reinstall the seat. Note the small crease down the middle caused by not replacing the 3 upper back hog rings with small zip ties. It's not a big problem because I can easily install the small zip ties there later. My previous DIY shows the disassembly processs which you can use in reverse to reassemble the whole thing:




The results:
The level of comfort from this new upholstery job blows away the previous mod while restoring the OEM look. The even padding throughout the seat back creates a smoother and more flush surface for your entire back. The flext plate eliminates the sharp stabbing points of the seat hardware and completely enhances the lumbar support. Another thing I realized is that while memory foam resists permanent compression better than regular foam, it is too soft and compresses way too much. Which means that your body's weight and warmth will compress it down next to nothing after a few minutes. The high density foam used here offers much better padding than memory foam for this kind of application. I am now satisfied that my car isn't gonna kill my back. I really hope carmakers like Toyota up their seat game but in the mean time I hope to spread the word that anyone can re-upholster their seats like this if they really want to, and you don't have to pay a shop a fortune to do it.