Technically down is washable. You do need to use the real big front loader at the laundrymat, and the right soap. It can be done. But it is certainly more of a project than synthetic.

You also need to be ready with one of your running shoes. Something needs to be thrown in the dryer with a down bag to help break up the clumps of down. Weight weenies, who only bring their bike shoes, will just have to borrow one or sit it out for awhile. It takes 5-6 hours to dry a down bag, and it is also good to break up the down clumps by hand every 20-30 minutes throughout the process.

I wash it when I get home in my own machine, using wool detergent, and hang it to dry in the shade. No problems with clumping, although my down jacket wasn't so lucky.

I don't know if I'd be keen to wash it mid-trip if I had to machine dry it, although if everything gets wet sometimes you don't have a choice. Having said that I've toured and camped in heavy rain and usually manage to keep the essentials dry.

130 grams

Different sleeping bags weigh different amounts. Temperature rating, type of fill, length and girth, basic shape (mummy style, rectangular or as one person mentioned quilts) all need to be considered for your question to have much useful meaning.

The above 130 gm refers to my silk liner which on warm nights is my sleeping bag.

I've always heard you're supposed to put a tennis ball in the dryer, with down. I've never tried it yet, with my down jacket, because I don't play tennis, and just never think of it, at stores. 😉
But I just scored an old North Face synthetic (100% polyester filling) bag yesterday, in like new condition. It has the old brown logo on a sewn-on patch, so probably from the early '80s, or maybe '70s. The bag and it's storage bag are both still super crinkly, like they were never washed yet. Oh, and long enough for my 6'2"-ish height, with a few extra inches. 😎

REI flash down bag. 1lb 10 oz.

That's what I always use and it works great. Washing down is not really technically difficult but does require a little more attention and a good bit more time.

1. Use a front loading washer.
2. Use woolite
3. Add extra rinse cycle.
4. Dry low-heat with tennis ball.
5. Keep drying till its dry & fluffy.

I have down items that are over 40 years old and still very usable.

I use a down MEC Merlin (-3 or -5°C) that weighs 824 grams including compression sack. I paid around 220$ CAD and was refunded half. Some bags were under filled so they offered to return it or a 50% refund. I've used it down to about -10°C on top of a NeoAir Xtherm.

Massdrop has nice quilts made by Enlightened Equipment.

I love my Sea to Summit Trek TKII. It is a down bag, the down is treated to be some what water resistant. It is not a mummy bag and it is not a rectangle bag, but it is a little of both. I really like the extra room the Trek line of sleeping bag offer. If you have a couple of the Trek bags they can be zip together to make one large bag for 2 which is really nice when the wife comes a long. Comes with a storage bag (never store a sleeping bag in a stuff bag/ compression bag), a bag for washing the sleeping bag and a compression bag. Mine is a large and it weighs about 2 lbs and 2 oz. Compress down to be smaller than a 2 liter bottle.

Summer...

OK with discomfort, and Mummy bag lack of interior space..? I went for comfort, Myself.

REI lists Bag weights..

Ended up going with the Kelty Cosmic Down 40. A 2-season Cosmic Down 40 sleeping bag with 600-fill DriDown.
Weight 1lb. 12oz.

Do some back yard overnights to find out what temp you comfy with. I sleep cold. For me it's not a 40*. But that's me. YMMV