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M&S

Heatgen™ Medium Thermal Long Johns

£20

Colour

Size

Also available in: Short Sleeve Thermal Top
Free standard delivery over £60

Product code: T148814N

About this style

These thermal long johns provide medium warmth with a regular fit, perfect for cooler days as a base layer underwear. The insulating brushed-back fabric offers breathability for lasting comfort, while comfort seams ensure a snug feel. Featuring Heatgen™ technology that helps generate and retain body heat when temperatures drop, making this undergarment ideal clothing for layering. M&S Collection: easy-to-wear wardrobe staples that combine classic and contemporary styles.

Medium warmth for wrapping up in moderately cold conditions.

Details & care

Style

Regular fit

Button fastening

Features

Thermal

Soft and cosy brushed fabric that keeps warmth in

Heatgen™ technology

lightweight and supersoft, designed to keep you warm when the weather gets chilly

Composition

50% cotton, 26% polyester and 24% viscose (exclusive of trimmings)

Care

Wash at 40°C

Do not bleach

Tumble dry medium temperature

Iron at medium temperature

Do not dry clean

Delivery, collection & returns

Delivery

Standard

UK Standard Delivery is available for £3.99 or free on orders over £60 (excluding furniture).

Nominated Day

UK Next Day Delivery and UK Nominated Day Delivery (excluding Northern Ireland) are available for £5.99 (excluding furniture)

Collection

Collect from store

Store collection is free on all fashion, home and beauty orders.

Returns

UK returns

Free

Exclusions apply

Full delivery and collection informationOur returns policy

Reviews (563)

4.7

72% Recommended this product

Mentions
16 November 2025MikeTL
Verified Purchase

Brilliant product

Yes, I recommend this

As an arthritis sufferer the warmth from these thermals is so good and helpful

Reviewer Ratings

Comfort

Excellent

Helpful?

Reviewer Ratings

Comfort

Excellent

16 November 2025LGJG
Verified Purchase

Good quality.

Yes, I recommend this

Good quality, nice fit. Very soft fabric and comfortable round waist.

Reviewer Ratings

Comfort

Excellent

Helpful?

Reviewer Ratings

Comfort

Excellent

16 November 2025Frinqui
Verified Purchase

Nice and warm

Yes, I recommend this

Nice and warm for under trousers when working outside

Reviewer Ratings

Comfort

Excellent

Helpful?

Reviewer Ratings

Comfort

Excellent

12 November 2025CHEPI1
Verified Purchase

Warm Soft and very cosy

Yes, I recommend this

Perfect to keep warm when the weather gets colder.

Reviewer Ratings

Comfort

Excellent

Helpful?

Reviewer Ratings

Comfort

Excellent

12 November 2025ILoveClothesandShoes
Verified Purchase

Great and long-lasting quality.

Yes, I recommend this

I have been buying Heatgen clothes from M%S for a longtime. I find them so warm, cozy and comfortable. They are wonderful to use in the winter months at home or when out. It saves using the heating all day. They are so good, I now have my husband buying them! I recommend them to anyone. Can you please provide more colours?

Reviewer Ratings

Comfort

Excellent

Helpful?

Reviewer Ratings

Comfort

Excellent

12 November 2025Froggy90
Verified Purchase

Good quality

Yes, I recommend this

Good for in my wheelchair during the cold winter months.

Reviewer Ratings

Comfort

Excellent

Helpful?

Reviewer Ratings

Comfort

Excellent

07 November 2025JDCMH
Verified Purchase

My go to for thermal underwear!

Yes, I recommend this

Always purchase thermal underwear from M&S, for my husband. Great quality, fit and price. As long as he’s cosy, that’s fine by me.

Reviewer Ratings

Comfort

Excellent

Helpful?

Reviewer Ratings

Comfort

Excellent

04 November 2025MisterHarry
Verified Purchase

Prefer the previous design

Yes, I recommend this

Material is good but possibly a few microns thinner than a few years ago, like the new style elastic waist band but not the one button fly front. The previous Y front style fly is probably more expensive to produce, more material and time.

Reviewer Ratings

Comfort

Average

Helpful?

Reviewer Ratings

Comfort

Average

30 October 2025BamfordL
Verified Purchase

Good quality

Yes, I recommend this

Bought these for my husband. Said they are very comfortable, keep his legs warm and good quality. Better than cheaper brands.

Reviewer Ratings

Comfort

Excellent

Helpful?

Reviewer Ratings

Comfort

Excellent

23 October 2025
Verified Purchase

Really pleased with the quality of this garment.

Yes, I recommend this

My husband hasn't worn these yet, but really pleased with quality of this garment.

Helpful?

12 October 2025chabod
Verified Purchase

Pleasantly snug fit

Yes, I recommend this

Need to be longer … good snug fit … need coloured options in maximum warmth apart from black, grey n white

Reviewer Ratings

Comfort

Good

Helpful?

Reviewer Ratings

Comfort

Good

11 October 2025GCOLeary
Verified Purchase

These will definitely keep me warm

Yes, I recommend this

I wasn’t sure about the colour but it’s fine for me

Reviewer Ratings

Comfort

Excellent

Helpful?

Reviewer Ratings

Comfort

Excellent

08 October 2025SabrinaBK
Verified Purchase

Super soft

It fits my 14 year old son perfectly and keeps him warm.

Reviewer Ratings

Comfort

Excellent

Helpful?

Reviewer Ratings

Comfort

Excellent

06 October 2025Margmania
Verified Purchase

A very good buy

Yes, I recommend this

Very good quality, hubby happy with the purchase and would buy again

Helpful?

21 September 2025Paul50
Verified Purchase

Nice and warm..

Yes, I recommend this

Ultra comfortable and cozily warm. Great fit without being too tight. I can honestly highly recommend this product!!

Reviewer Ratings

Comfort

Excellent

Helpful?

Reviewer Ratings

Comfort

Excellent

25 April 2025callmeD
Verified Purchase

Value for money

Yes, I recommend this

When it came time to replace my well-worn thermal pants, I always chose M&S. The pants are well made and value for money.

Reviewer Ratings

How did it fit?

True to size

Helpful?

Reviewer Ratings

How did it fit?

True to size

08 April 2025CherrB
Verified Purchase

Long johns

Yes, I recommend this

My husband is elderly and finds it difficult to keep warm, but the long johns solved that problem, he loves them

Helpful?

19 March 2025Tree36
Verified Purchase

Usual great quality.

Yes, I recommend this

These long johns were purchased for the recent very cold spell. They were brilliant in keeping my husbands legs warm. Great fit.

Reviewer Ratings

Quality

Excellent

Value for Money

Excellent

Style

Excellent

How did it fit?

True to size

Helpful?

Reviewer Ratings

Quality

Excellent

Value for Money

Excellent

Style

Excellent

How did it fit?

True to size

17 March 2025cornedbeef
Verified Purchase

Warm but not comfy

Warm but has really big internal seams which mark the legs quite badly. I actually wore them inside out which was a lot more comfy

Reviewer Ratings

Quality

Good

Value for Money

Good

Style

Average

How did it fit?

True to size

Helpful?

Reviewer Ratings

Quality

Good

Value for Money

Good

Style

Average

How did it fit?

True to size

08 March 2025Fabrice576
Verified Purchase

Perfect balance between warmth and bulk

Yes, I recommend this

Really like these long johns , perfect warmth to bulk ratio Particularly like the button opening as it allows wearing regular underwear too Very soft with no seams discomfort and washes well

Reviewer Ratings

Quality

Excellent

Value for Money

Excellent

Style

Excellent

How did it fit?

True to size

Helpful?

Reviewer Ratings

Quality

Excellent

Value for Money

Excellent

Style

Excellent

How did it fit?

True to size

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