I have an Alpkit Hunka bivi bag but found the size to be a bit restrictive. If I put my mat inside and rolled over in my sleep then everything would move with me so i'd end up with no mat beneath me. I also found that if I have to wear my down jacket to sleep in then the mat just will not fit inside the bivi bag.
A little while ago people were talking of using tyvec for various things and I managed to get hold of some from MM-on-point (thanks again) from the classifieds on here.
I wanted something big enough to take my new Exped Lite down mat, let me roll over without moving the mat and be able to wear my down jacket to sleep, this is the result which weighs in at 225g.
Bivi bag with mat and sleeping bag inside.

Tyvec Bivi Bag 001 by youngray50, on Flickr
Envelope style hood (will always be used under a tarp so not worried about being able to close the opening up tight).

Tyvec Bivi Bag 002 by youngray50, on Flickr
Envelope hood closed.

Tyvec Bivi Bag 003 by youngray50, on Flickr

Seams where made using strong double sided carpet tape and are 2" wide. I was going to sew them as well but found the sticky tape kept gumming up the needle and snapping the thread on the machine, I think the seams will be strong enough as they are.

Nice work that. Been meaning to have a go at this as well for exactly the same reasons. I read somewhere that tyvek can be pretty noisy and stiff until you give it a go in the washing machine.

TheBrownDog wrote:Nice work that. Been meaning to have a go at this as well for exactly the same reasons. I read somewhere that tyvek can be pretty noisy and stiff until you give it a go in the washing machine.

Washed it twice on a short wash/low temp then ironed it on a very low temp along the seam lines where the tape was going. I'm happy with the result, I may add some Velcro along some of the hood line to help keep it closed when needed.

Looks good ray. Love you our list of MYOG is impressive.

Love you our list of MYOG is impressive.

Is that written in some kind of code Mike?

Bloody predictive text and my cack handed typing.
Meant to say "your list of MYOG is impressive" without the declaration of love.

pushbikemike wrote: without the declaration of love.

Ooh, you fickle heartbreaker .

pushbikemike wrote: "your list of MYOG is impressive"

Necessity, mothers and invention.