Wearing just one extra layer under your running outer makes a big difference in warmth. And, it doesn't get in the way of your arm swing, so I don't think it will affect your run. Women's M size. Worn a few times. It says it's packable, so it should be compact... I think. Lightweight and packable Nike Aeroloayer black quilted vest. - Brand: Nike - Model Name: Aeroloayer - Features: Packable Garment - Color: Black - Design: Quilted Thank you for looking.