Lori writes:

While in several fabric shops in the NY garment district, I saw bolts labeled sponged wool. I could feel the difference in the fabric, but was surprised at how different the wools were (various weights, patterns, and actual composition; not all were 100% wool) and yet still were labeled sponged wool. I’m not sure what that means. Since then, I have asked several instructors and experienced seamstresses but no one seems to know. I tried researching but haven’t found it.

What is the process used to sponge wool? What is the advantage? Does it change just the texture or change something else about the fabric (make it stronger)? Are there any limitations in care due to this treatment? Thank you for any help you can give me.

Sponged wool has been pre-treated for shrinkage. How effective the process can be (based on personal experience) is open for debate. Most sponged wool is used in manufacturing because there isn’t an easy way to preshrink lengths of wool like you can in home sewing. You can sponge at home but the difference between industry vs home is that sponging at home is a cold shrink process. In industry, sponging is a heat shrink (steam) process.

There are various kinds of sponging. One type uses a large drum with holes in it, imagine a dryer drum. The fabric is wound around the drum and steam is forced through the holes. Another kind involves a take up on one end and the bolt of fabric on the other. The fabric is unrolled and rolled from one end to the other, along the way passing over a steam pot. One variation is the steam pot followed by a vacuum table which pulls the water out (illustrated above), drying the fabric. Critical in all of these methods is setting machine tension. If the roller motors aren’t calibrated properly, the tension is too high preventing shrinkage. Too lax a tension and the goods on the path can be drenched in the steam pot and be wrinkled on the take up roller.

Sponged wool is a premium product; last I checked, it costs about 20% more per yard. I would be hesitant to say the nicer finish and pile is strictly due to the sponging process because it depends on so many factors, least of which is a side to side comparison although some designers won’t work with any other kind. Because of the premium cost, I would imagine it is better quality goods that are pre-selected for sponging. However, a manufacturer can have any wool sponged after the fact by taking it to someone who does finishing or a laundry (or a dyer even) that specializes in serving the garment trade if they have the equipment. Many wool vendors have relationships and will arrange to have it done for the customer before shipping the goods.

Cold shrinking:
You can use the cold shrink method at home although this process is not likely to raise a nap if you like that look. The process is to drench a bed sheet, fold it in half and lay it out full length on the floor. Lay the wool on top of the sheet starting about two feet down from one end of the sheet. Fold that exposed sheet end onto the wool. Then fold the whole length of goods loosely, the point is to have a layer of wet sheet interlaced with wool. Store put the bundle someplace and let it sit for… I don’t remember how long, until it dries or nearly so. Living in the southwest, I’d likely cover it with plastic to keep it wetter longer, at least a day or so. The last time I did this I was living in Dallas where it is more humid. Don’t make me swear to it but I think a 48 hour period was prescribed.

Lori responded:

I knew I had finally asked the right person! How lovely to know the process and what it does; now wish I had been braver about buying some so I could examine it more closely. There were many at Paron’s in the 50% off room, and I noted that several had a ‘spongy’ feel or almost like a bit of loft. Now I wonder if that was more my imagination in trying to figure out the term.

Your use of ‘imagine a dryer drum’ led me to two other thoughts. Pamela Erny had posted a method of preshrinking wool at home. It strikes me as being a sort of home version of sponging.

Pam’s version is interesting, I haven’t seen that one before. It seems akin to a minimalist process of boiling wool -which is itself, an extreme version of sponging.

Speaking of boiled wool, I don’t know how that is done in industry but I may look it up later. We buy boiled wool as is; I haven’t known of anyone getting regular wool and having it boiled. Which is not to say you can’t do it fairly easily at home. I’ve done it by washing and drying wool repeatedly. It’s pretty hard to mess up but you want to be sure you don’t make the wool brittle by stripping out what remains of the natural oils with detergent and heat. I like to use shampoo (in one cycle) and replenish moisture with hair conditioner for subsequent cycles. Using a hot dryer is fine as long as you do the latter but avoid Johnson & Johnson baby shampoo; it is very astringent.