When/why would I use wash-in DWR as opposed to spray-on?

Note to self: use Google to search site, you may have posted on this before! Oops.

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=28952

Guess I've also revealed how infrequently I do my DWR.

1. use NikWax wash-in DWR
2. dry garment in a dryer at medium heat
3. spray on Revivex

Best home DWR process I've ever found.

and Eric likes to answer this question from you as well. lol!

So, Eric, you don't worry about having DWR on the inside of a garment?

John,

It weems the Nikwax DWR has no effest (that I can tell) on the inside of a garment in terms of sweat "beading" on it. Never saw it happen.

But I do know these two good DWR treatments seem to work best together.

Since the increasing exposure we have to chemicals may be a causative factor in health problems I prefer to reduce exposure when possible. I use the spray on for that reason.

Do I know there is a any real concern here? No, but I prefer to be cautious in regard to my health. Except of course when it comes to hiking alone, hiking at night, climbing up steep places, going out it blizzards, going out in bear & mountain lion country, etc. :)

I've seen it mentioned on here that DWR retreat meets only stick to areas where old DWR is still present. I don't know if this is true or not. But if so, that would seem to indicate that the wash-in approach would not apply a coating to the inside surface of your clothing (unless it was it there originally by the manufacturer).

Some have mumbled that unlike wash-in, spray-on has less impact on the membrane.
I don't know one way or the other.

Off on a slight tangent, per Mr. Nisley, 2/18/2010

"A DWR works by creating a low attraction (surface energy) between water drops and the fabric. This allows the water drop to roll off rather than flatten out and stick to the surface.

"The fluorochemical DWR molecules on the outer surface of your eVENT jacket contain a vinyl or acrylic polymer that sticks to the fabric. Attached to this backbone are little perfluoro tails (side chains) that are normally repelled from fabric surface by polar forces and stick up into the air. The little tails are what creates the low surface attraction to the water molecules and keeps the DWR working. Sustained exposure to water or abrasion will cause the tails to flatten out and the DWR to stop working. Heat of at least 140F is needed for about 15 minutes to create enough molecular motion for all of the tails to fully stand back up again. [ Throw it the dryer for 15 minutes and remove immediately. gm]

"… For others using Nikwax or a Silicone DWR, heat will provide no benefit. In order of durability the above DWR type is the most durable, silicone is next, and wax is last."

So I wouldn't mix-and-match fluoro's with wax or silicone.

They both leave a layer a few atoms thick on top of the old DWR. No known health of breathability effect unless you put them on with a shovel.

Wash in is easier. Spray on works on things you can't wash, e.g. some hats.

Use both if you like I guess.

NB DWR generally likes tumble driers but some fabric (e.g. Polartec Neoshell) doesn't. Expensive mistake to make.