I've been icefishing for over 10 years...in all kinds of weather from 10C to -30C. Each day is a little different.
Some days starts off cold and windy, then the sun comes out and it is mild and calm, and closer to the evening, it gets windy and cold again.
There are times a snow squall will creep up on you on an otherwise very nice day. It can get down right miserable within 15 minutes.
There are days you walk 2 minutes on the ice and you're fishing, and the other days you hike 3km in knee deep slush.
Fishing on the ice is cold, and wind can make it very uncomfortable. That makes people often "overdressed" as a precaution.
What they fail to remember is that icefishing is also a very physical activity. Even simply walking for 30 minutes to your spot with a little bit of gear on you is a lot of work. Your body heats up quickly and soon you'll be sweating. SWEAT IS YOUR ENEMY! It may feel warm when you are active, but once you settle down at your spot, all that moisture next to your skin will quickly remove heat from your body.
When I'm icefishing, I usually dress in 4 layers. I don't have a polypropylene underlayer. I wear wool underwear instead. Wool does absorb heat, but it also wicks moisture away from your body. Wool is a hollow fiber, and as such, it will keep you warm even when wet. That is why I prefer to have wool next to my skin.
Never have cotton next to your skin!!! I've done it before as a newbie...and it was a big mistake. Cotton soaks up moisture and it is stored. Having cotton next to your skin will make you very cold very quick.
Air space is actually what will keep you warm the most. A thin layer of air between each layer acts as an insulating layer. Heat conduction is slower through air, thus, heat loss is much slower through air. That's why a lot of synthetic materials are fine fibers with hollow cores to increase air space.
Although a air/water tight outer layer is nice, make sure you have some way to wick away moisture from your body, and that moisture is not trapped inside you and cannot escape. Trapped moisture will condense in the cold, and when you stop moving, that condensation will stick to your clothing layers. Again, moisture is your enemy and you do not want to accumulate any of it!
When I take people out icefishing the first time, I always tell them to dress layers, but I tell them not to put on all the layers. I tell them to bring a backpack or duffel bag where they can keep certain items when not in use.
Here is my usual routine...
1) At home, I will put on the wool under layer, and then a fleece hooded sweater and a fleece pants. That's all I'll wear from home to the parking area of the fishing spot. You DO NOT need to put on jackets! The car will keep you warm enough. If you put on your jacket already in the car, your body will get too warm, and you will already start sweating...GAME OVER!
2) I put on a pair of cotton socks for the drive. Don't put on your wool socks or thermal socks yet! I also just wear a simple pair of shoes without any insulation so that you don't sweat in your shoes. There is NOTHING worst than cold feet...except maybe frozen hands...but cold feet can end you day quickly.
3) In the car, I try to keep it a cool temperature, just warm enough not to be cold, but cool enough so I'm not sweating. My theory is that your body will self regulate temperature and adjust to a temperature range. If I keep the car temperature cool, my body has at least an hour to adjust to cooler temperature, and as such, my day will start off ready for even colder temperature. I always find it interesting that in the spring, we're always wearing very little clothing at 10C, but in the fall, the same 10C will have us bundling up already...that's because in the fall, the body was used to warm weather of summer and it has not adjust to dealing with cold yet, while in the spring, our body was used to much colder weather and the slightly warmer weather is more than the body was used to dealing with. Similar concepts apply even to a short drive. Try it...trust me.
4) Keep all your clothing items inside the car! There is nothing worst than putting on a cold floater suit or cold jacket and snow pants!
5) Once I get to my fishing location, then I start changing. The first thing that I'll do is to put on a pair of dollar shop cotton winter gloves. There is nothing worst than cold hands other than cold feet. With frozen hands you can't do anything...so the cotton winter gloves are the first to go on. Next, cover your head. This is where the hooded sweater is important. Put the hood on...but not your hat! Most of the heat is lost through your head...but if you put your hat on too early and sweat in your hat, then you'll have a cold head for the rest of the day!
6) You have to remember that you have a walk out. Depending on the distance and terrain, you have to keep that in mind. I usually will put on my floater suit, but I only put on the legs part of the suit. I keep the top part OFF! I often find it way too warm hiking out with the suit fully on. At this point, you can put on your scarf if you need, depending on the day, I may even put on a balaclava as a wind block layer. You can also put on your insulated boots.
7) But you say...you're still in your cotton socks! Isn't that bad? No...at least not with what's to come. So now you're somewhat dressed...but still have a lot of layers off. As I walk out, pulling a 30-40lb sled, I'll start to get warm. If it is not too windy, I'll soon remove my hood and scarf. This is where you need a backpack or duffel bag to hold your clothing items (plus others that you'll put on later). Your hands may soon need an outer glove layer, so you can start putting on your gloves ON TOP OF your dollar shop mittens. Yes, your feet will start sweating and the cotton socks will start absorbing the moisture. It's okay at this point.
8) Once you get to your spot, there is more to do. You need to auger holes...and if you have a shelter, you need to set it up. All of that are high energy activity. At this point, I may even start removing more layers. I could step out of my floater suit so I stay cool.
9) Once I get everything set up, now I'm ready to settle down and fish. I don't start putting on all the layers in a hurry though. As my body cools, I start putting them on as necessary. The first thing that I'll do is to switch out my cotton socks for a new dry pair of wool socks! See how it works? You wear the cotton socks on the way out to soak up all the moisture, then you remove it on the spot to fresh new wool socks so now you will have warm feet for the day!
10) Then I'll put my hat and scarf back on when it start to feel a little warm. Since you didn't sweat in your hat (I hope not), it will keep you warm for the day. The sweat that you may have are on the hood, not on your hat. Later on, you may find you need to put on an extra wool sweater, or in my case a down vest to keep my body core warm. Even at this stage, if it is not too cold, I will keep the top of my floater suit off. I want as much of the moisture to escape my body as possible...if there is any.
11) Once you have settled down enough, and even with the layers you feel a bit cold, then put on your outer layer at the end. Now, if it is a blowing blizzard out there, you have no choice but to put on your wind block and waterproof outer layer from the get go. In that case, I keep the outer layer unzipped so moisture and heat can escape so I don't overhead and build moisture.
12) If your feet still feel a little cold, you can put on an extra layer of thermo socks or wool socks. A lot of people forget about their extremities. You still need to use the same layering concept with your extremities as you do with your body core. Although I do wear cotton winter gloves as a liner next to my skin, the hands rarely sweat. I find they get cold from touching snow and ice and gets wet. So usually I will have 3-4 pairs of these cotton gloves to change them out and allow them to dry (if I'm using a heater) throughout the day. I will always have a outer glove that is waterproof and windproof. Although mittens ARE warmer, they are not at all practical when icefishing. For me, always having dry cotton glove liner is always better than having just one pair of mittens.
It is a bit complicated and troublesome...but following the concept of regulating body temperature and moisture and layering as necessarily (as opposed to too early or when not needed) has helped me to fish all day in -20C without any issue.
There is method to my madness.
Oh...and don't fall for the trap of neoprene gloves!!! Neoprene is terrible. Yes, it is waterproof, but the neoprene has little pores that will soak up some water...and then freeze onto the glove. Neoprene also doesn't breath, so the moisture in your hands gets trapped. Neoprene also conduct heat well...meaning there will be a lot of heat loss. Even insulated neoprene gloves are bad. Instead, wear a fleece outer glove or a good pair of wind and waterproof snowmobiling gloves. They are a little more expensive but so much better! Dexterity of those gloves is also far superior than a pair of cold neoprene gloves which are very, very stiff once cold.
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Age does catch up to you...even as young as 30. 