I meant that I will use the prewashed fabric for backing and am worried about using unwashed fabric for the top of the quilt. Was worried that once the finished quilt is washed the top might shrink more than the back. Does that make sense? By the way, after two washings and vinegar in the rinse water 2 people with very sensitive noses found them odor free. Will try the hot iron - Tartan, thanks for the tip

If you are using it mostly for backing I don't think it will be a problem. If you are mixing with unwashed fabrics in a quilt top I would check to see if the weave seems to be about the same. Could also check by washing pieces of the unwashed fabric in a little pan of water, measuring before and after washing to see if the unwashed fabric shrinks. Lots of extra trouble but may be worth it.

If you have washed the fabric and it removed the odor, makes me feel yucky thinking about the smell; then I would think you are good to go.

I prewash every piece of material. Small pieces go into a lingerie bag or 2 or 3. Nicotine odor is hard to get out. Depending on how large the smaller pieces are would depend on whether I wanted to fool with them or not. I would be insulted if someone made me a quilt and it smelled of smoke. That's me. If you can find some one who has not been around smoke in a while ask them to take a whiff. The slightest hint of smoke will be made stronger when it dries.

If you are wondering whether you can use prewashed backs with non-prewashed tops, quit worrying. Don't try washing the fabric for the tops. After you get your project made and laundered, what was preswashed and what wasn't won't make a bit of difference. Been there, done that. froggyintexas

I think it really just depends on the fabric. I've had some fabrics that I purchased that are labeled "do not pre-wash". Others I've been glad I did because there was a noticeable amount of shrinkage.
The other issue you have to think about is that there are those very rare fabrics that will bleed the first time you wash them -- so just be sure that when you launder the finished quilt that you wash it on cold & if you have a lot of intense colors maybe toss in 1 or 2 of those Shout Color Catchers.

I have a related question, am new to this board and don't have permission to start a new thread, so hopefully replying to this is how I am supposed to ask a question. Thanks!
QUESTION:
I am relatively new to quilting and have heard conflicting advice on pre-washing fabrics. I was taught by my grandmother and aunt to pre-wash, but when visiting a quilt shop and discussing pre-washing fabrics with a friend, the owner of the shop overheard the conversation and told me that pre-washing fabrics is an antiquated technique and that it's completely unnecessary with today's fabrics. I mentioned that people often use fabrics from large stashes that may have been purchased at various times, even different decades, but she still asserted that it wasn't necessary. I just finished piecing a quilt made mostly of batiks and dark solids (all cotton, recently purchased), which I did not pre-wash, and now am coming across a lot of blogs that say pre-washing is essentially a must. Now that I have my top pieced, is there anything I can do to minimize bleeding once the quilt is finished (soak in a tub perhaps)? I am less concerned with shrinkage, because I like that look, but that may even become an issue. The quilt is a gift that is intended to be used with frequency. If I finish the project without any sort of washing now that it's pieced, is my recipient going to have a mess on their hands or come out with a completely different quilt once washed? Thanks for any advice you have!
Examples of what I'm reading online:

• For: "It prevents vibrant dyes from spreading onto other fabric. Some bright colors, like reds and purples, can run and bleed when they are washed. This can be very devastating if it happens to a finished quilt."
• Against: "With today’s quality fabrics and dye, bleeding is not much of an issue. Most manufacturers realize that a vast amount of quilters do not prewash, so they ensure that the dyes are set completely."

I still think you should air it out in the sunshine on a good weather day. Nothing like mother earth's wind to remove the last of the odor. I too have mixed fabrics. If your top is totally unwashed or a mixture of fabric, I don't think you will have a problem. Good Luck.