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Midweight thermal sleeping bag liner with Thermolite Pro insulation, stretch-knit fleece comfort, integrated armholes and FIR heat-reflective technology.
Midweight thermal sleeping bag liner with Thermolite Pro insulation, stretch-knit fleece comfort, integrated armholes and FIR heat-reflective technology.
Sea to Summit

Sea to Summit Reactor Midweight Liner Large Beluga

£49.50 £55.00 10% off
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Pre-Order

With Pre-Order, you can purchase the latest items added to our store in advance of them arriving with us.

Your Pre-Order is prioritised (at no additional charge); meaning that as soon as the product arrives with us, we can wrap it straight back up; ready for collection via Click & Collect or despatch to you — it often never even hits the stock room shelves!

Pre-Launch

With Pre-Launch, the date when we expect to receive the product ourselves is still a little too hazy to be confident in accepting Pre-Orders.

So, instead, you can submit your email address against the item you are interested in and we will email you as soon as stock arrives on the system.

Estimated Delivery & Collection Dates

Estimated Delivery & Collection Dates are given on Pre-Order and Pre-Launch products. They are for indication purposes only and can change at any time without notice.

The dates we provide are based on indications given by our suppliers. Whenever we get updated information from our suppliers we will endeavour to update the Estimated Delivery & Collection Dates provided on product pages.

We estimate this will be ready for despatch to you or collection via Click & Collect on Undetermined
Earn Rewards
When you purchase this item, you will earn of rewards points to spend on your next purchase from us. You can spend your Rewards balance in-store & online.

90-day returns period

DPD Returns Portal
We hope that you are perfectly happy with your order from Trekitt, but we understand that sometimes you may need to return an item. We offer a 90-day returns period from the date of purchase and aim to process all returns within 48 working hours of receipt. During exceptionally busy periods, returns may take up to 7 working days to be processed.

We do not offer a free returns service. If using the DPD Returns Portal, a charge of £5 will be deducted from your refund when processed. Returns from Highlands and Islands using theDPD Returns Portalwill deduct £15.50 from the order refund. Large DPD returns will have £6 deducted from their refund. (Specifications are over 5kg, and over Length of 30cm x width of 30cm and height of 10cm). If customers are returning items using their own postal service, and our returns form, all customers are responsible for any postage costs when returning any goods (excluding warranty returns).
For your convenience, follow here to theDPD Returns Portalto submit a return or click the button below. Alternatively, to arrange return postage for your items. Please use our warehouse returns address (Returns, Unit H&J, Moreton Business Park, Hereford, HR4 8DS) when completing the Returns PDF form below.


We are not liable for delays once an order has been dispatched. However, we will always work with the courier to assist in resolving any delivery issues where possible.
If an order has not been received, customers must contact us within 14 days ofdispatchso that we can investigate and assist accordingly.

If you have returned an item using the DPD returns portal and have not received confirmation of your refund, you must contact us within 14 days of dispatching your return so we can investigate. After this period, we may be unable to investigate or raise a claim.
We do not offer a free returns service. Customers returning items using their own postal service and our returns form are responsible for any postage costs when returning goods (excluding warranty returns).
To arrange your return, please complete the Returns PDF form and send you item to our warehouse at:
Returns
Unit H&J, Moreton Business Park
Hereford
HR4 8DS
Thank you for your patience while we improve our returns service.



The Trekitt Returns Policy Includes...
A 90 day return period and the Trekitt 2-year Common Sense Guarantee.

Exemptions & Surcharges
PPE (Facemasks, Climbing Equipment etc. ), Food Goods, Accessory Cord, Socks & Underwear can only be returned if they have not been worn and/or removed from their original packaging with all swing tags still attached. If there is any sign or possibility that the goods have been used, tampered with or contaminated in any way, then we cannot accept a return on the grounds of consumer safety. Zips are typically not covered under a manufacturer's warranty.

Please take care when packaging your returning order as customers will be liable for any exceptions or surcharges incurred for incorrectly packaged returns. You will be informed via email of the value of the charges which will be deducted form your refund amount.

The above does not affect the Consumer Contract Regulations. Click here to read more.

I want to return/exchange an online order
I want to return an unwanted item I want to return a faulty item under warranty I want to Exchange an item
Post it back to us Bring it back to us

To return an item to us, you must first:

  • Ensure the item is unused and in its original condition (including all label, tags and Boxes) and in a resellable condition
  • To arrange return postage for your items. Please use our warehouse returns address (Returns, Unit H&J, Moreton Business Park, Hereford, HR4 8DS) when completing the Returns PDF form here.
  • Appropriately package your item in protective packaging, failure to do so will invalidate your rights to a full refund or return (including footwear boxes which can be damaged in transit/customer care if not protected)
  • Please take care when packaging your returning order as customers will be liable for any exceptions or surcharges incurred for incorrectly packaged returns. You will be informed via email of the value of the charges which will be deducted form your refund amount.

Trekitt Returns,
Unit H-J,
Moreton Business Park,
Hereford,
HR4 8DS

Please ensure the service you use corresponds to the size/weight/value of the item. We regret to inform you that we cannot be held responsible for returned goods that become lost or damaged in transit. We therefore strongly recommend that you use a recorded/insured delivery service and keep a record of this and track your item. Once it has arrived at our warehouse, please wait the advised 48 hours for your refund which you will be notified of with a refund receipt sent to your account email. If you have not heard anything after this then please reach out to our Customer Support Team [email protected].

You can also return internet purchases at the Trekitt Service Centre in Hereford. To speed things along, please bring the Sales Invoice we sent via email as proof of purchase.

If you choose to receive a refund, this will be processed separately by our Customer Support Team.

You may exchange product(s) at the shop for Goods of an equal or higher value for which you will receive a new receipt.

Please note:
PPE (Facemasks, Climbing Equipment), Food Goods, Socks & Underwear can only be returned if everything is exactly as it was received. Packaging and labelling must be intact, and underwear must be unworn. If there is any sign or possibility that the goods have been used, tampered with, or contaminated in any way then we regret that we are unable to accept a return on the grounds of consumer safety.

This does not affect Consumer Contract Regulations.

Post it back to us Bring it back to us

If you feel that your item is defective/broken/faulty and it is still under warranty, please contact our Customer Support team ([email protected]) with as much information as possible with regards to the fault, including photos if applicable.

In return, they will supply you with a Returns Authorisation Number (RAN), a Returns Form and a FREE postage label. Please complete the returns form with as much detail as possible and include it with your item.

Download our Returns Form.

Trekitt Returns,
Unit H-J,
Moreton Business Park,
Hereford,
HR4 8DS

We cannot make any decisions before inspecting any claim. Should the item be found genuinely faulty, we aim to reach a fair and agreed solution, which may be a refund, a replacement or a professional repair.

Please note: We may need to send items to the original supplier, or a fully certified testing company. This process can take up to four weeks or longer during busy periods.

THIS BIT IS IMPORTANT! - To ensure your Warranty Return goes smoothly, please ensure all items are in a clean, dry condition and free from dirt. Any items that do not meet the above criteria will be sent back to you for health and hygiene purposes or you may be contacted asking if you would like us to clean it for you, where a cleaning charge will be applied with a minimum charge of £25.00.

Failure to follow the Warranty Returns procedure may significantly affect our ability to process your return and cause a delay in issuing your refund/replacement/repair.

You can also return internet purchases at the Trekitt Service Centre in Hereford. To speed things along, please bring the Sales Invoice we sent via email as proof of purchase.

If you choose to receive a refund, this will be processed separately by our Customer Support Team.

You may exchange product(s) at the shop for Goods of an equal or higher value for which you will receive a new receipt.

Online Bring it back to us

We do not offer exchanges. Instead we ask you kindly to complete a new order for the desired replacement and return the unwanted Good(s) for a refund. We acknowledge that this might seem more complicated, we can assure you it is by far the most efficient and fastest way to ensure that you receive the goods you require.

Any returns sent back requesting an exchange will be refunded in line with our returns process.

You can exchange internet purchases at the Trekitt Service Centre in Hereford, to speed things along please remember to present the sales invoice supplied by us in respect of such Goods as proof of purchase. You may exchange product(s) at the shop for Goods of an equal or higher value for which you will receive a new receipt.

Book an appointment
When will I receive my refund?
I paid by card I paid using PayPal

Once our Returns Team has processed your refund, you will receive a new e-receipt showing the returned item(s). After this you should expect to see your funds back in your account within 3 to 5 working days, depending on how your card provider processes refunds.

Refunds can only be made to the original payment method and are normally processed within 2 working days, however, during busy periods they can take up to 7 days.

Once our Returns Team has processed your refund, you will receive a new e-receipt showing the returned item(s). After this you should expect to see your funds back in your PayPal account that same day.

Refunds can only be made to the original payment method and are normally processed within 48 hours, however, during busy periods they can take up to 7 days.

What is the Trekitt 2-year Common Sense Guarantee?

We love this business and take great care personally selecting the products we sell. We are confident that the kit we have chosen is the best currently available.

That is why we offer our Trekitt Common Sense 2-year guarantee on every product we sell!

Therefore, if within 2-years a manufacturing fault develops in the materials or construction of a product that we have sold you, we guarantee to sort it out. We aim to reach a fair and agreed solution, which may be a refund, replacement or a professional repair.

The "common sense" bit. Please don't send us kit that has been used and abused and is completely worn out, and then expect us to replace it. Stuff does wear out, it's a fact of life, however if you feel that your purchase is genuinely faulty please get in touch with us at [email protected]

Please note:
PPE (Facemasks, Climbing Equipment), Food Goods, Socks & Underwear can only be returned if everything is exactly as it was received. Packaging and labelling must be intact, and underwear must be unworn. If there is any sign or possibility that the goods have been used, tampered with, or contaminated in any way then we regret that we are unable to accept a return on the grounds of consumer safety.

This does not affect Consumer Contract Regulations.

What does "90 Day Returns Period" mean?

We offer an 90 Day returns period provided the items are returned in the original condition that you received them, including all labels and packaging intact.

Please note:
PPE (Facemasks, Climbing Equipment), Food Goods, Socks & Underwear can only be returned if everything is exactly as it was received. Packaging and labelling must be intact, and underwear must be unworn. If there is any sign or possibility that the goods have been used, tampered with, or contaminated in any way then we regret that we are unable to accept a return on the grounds of consumer safety.

This does not affect Consumer Contract Regulations.

Consumer Contract Regulations (CCR)

What are the Consumer Contract Regulations?

Under the "Consumer Contract Regulations, you have the right to cancel an order for goods made at a distance. These rights start from the moment you place your order and ends 14 days from the day you receive your goods.

Your right to cancel

Your right to cancel an order for goods starts the moment you place your order and ends 14 days from the day you receive your goods.

This 14 day period is the time you have to decide whether to cancel, you then have a further 14 days to actually send the goods back.

Your Right to a Refund under CCR

You may get a refund within 14 days of either, the trader getting the goods back, or you providing evidence of having returned the goods (for example, a proof of postage receipt from the post office), whichever is the sooner.

A deduction can be made if the value of the goods has been reduced as a result of you handling the goods more than was necessary. The extent to which you can handle the goods is the same as it would be if you were assessing them in a shop.

Refunding the cost of delivery

The trader has to refund the basic delivery cost of getting the goods to you in the first place, so if you opted for enhanced service e.g. guaranteed next day, it only has to refund the basic cost.

Exemptions

There are some circumstances where the Consumer Contracts Regulations does not give you a right to cancel. These include CDs, DVDs or software if you've broken the seal on the wrapping, perishable items and tailor-made or personalised items. They also include goods with a seal for health protection and hygiene reasons that have been broken or tampered with, e.g. Climbing Equipment and PPE.

My goods are broken

If you feel that your item is defective/broken/faulty and it is still under warranty, please contact our Customer Support team([email protected])with as much information as possible with regards to the fault, including photos if applicable.

We want to reduce our impact on the environment as much as possible, the first step for this is reducing our waste. Therefore, please note that we will always offer a professional repair in the first instance; if the product can be repaired.

This may involve your product being sent back to our suppliers or to a professional repair company. Please note that due tovaried procedures, warranty claims and repairs can take between 2 and 4 weeks to be concluded

Consumer Contract Regulations (CCR)

What are the Consumer Contract Regulations?

Under the "Consumer Contract Regulations, you have the right to cancel an order for goods made at a distance. These rights start from the moment you place your order and ends 14 days from the day you receive your goods.

Your right to cancel

Your right to cancel an order for goods starts the moment you place your order and ends 14 days from the day you receive your goods.

This 14 day period is the time you have to decide whether to cancel, you then have a further 14 days to actually send the goods back.

Your Right to a Refund under CCR

You may get a refund within 14 days of either, the trader getting the goods back, or you providing evidence of having returned the goods (for example, a proof of postage receipt from the post office), whichever is the sooner.

A deduction can be made if the value of the goods has been reduced as a result of you handling the goods more than was necessary. The extent to which you can handle the goods is the same as it would be if you were assessing them in a shop.

Refunding the cost of delivery

The trader has to refund the basic delivery cost of getting the goods to you in the first place, so if you opted for enhanced service e.g. guaranteed next day, it only has to refund the basic cost.

Exemptions

There are some circumstances where the Consumer Contracts Regulations does not give you a right to cancel. These include CDs, DVDs or software if you've broken the seal on the wrapping, perishable items and tailor-made or personalised items. They also include goods with a seal for health protection and hygiene reasons that have been broken or tampered with, e.g. Climbing Equipment and PPE.

DPD Returns Portal

Sea to Summit Reactor Midweight Liner Large Beluga

Season:AW26

Brand:Sea to Summit

Code:53303

Sea to Summit Reactor Midweight Liner Long Overview

The Sea to Summit Reactor Midweight Liner Long is a versatile thermal sleeping bag liner designed to improve warmth, sleeping comfort and sleeping bag protection during backpacking, camping and winter adventures.

Built using stretch-knit Thermolite Pro fleece fabric, the liner moves naturally with the body during sleep while integrated armholes provide unrestricted movement for side sleepers and restless sleepers alike. Using hollow-core fibre construction and Far Infrared (FIR) technology, the fabric traps and reflects body heat, increasing sleeping warmth by up to 6°C / 11°F without the bulk of a heavier sleeping bag.

Unlike a traditional sleeping bag, the Reactor Midweight Liner is easy to clean, quick-drying, and highly adaptable to changing conditions. HeiQ Fresh odour-control treatment helps maintain freshness during multi-day trips, while regular use of the liner reduces the need to wash your sleeping bag frequently, helping preserve insulation loft and long-term thermal performance.

Its balance of warmth, freedom of movement, and lightweight packability makes it a practical addition for backpacking, hut trips, bikepacking, and colder overnight camping conditions.

Best for

  • Backpacking
  • Camping
  • Winter camping
  • Hut trips
  • Bikepacking
  • Travel
  • Cold-weather sleep systems

Materials and Construction

Thermolite Pro Fleece: Midweight Thermal Performance

The Reactor Midweight Liner uses Thermolite Pro and Thermolite EcoMade fibres designed to improve warmth retention while maintaining good packability for backpacking and travel use.

The hollow-core fibre construction traps warm air efficiently to improve insulation performance without excessive weight or bulk.

FIR Technology: Heat Reflection

The Thermolite Pro fabric incorporates Far Infrared (FIR) technology designed to reflect body heat back towards the user.

This improves thermal efficiency within the sleep system and contributes to an added warmth increase of up to 6°C / 11°F during colder overnight conditions.

Stretch-Knit Fleece Construction for Freedom of Movement

The stretch-knit fleece fabric moves naturally with the body rather than restricting movement during sleep.

This improves comfort for side sleepers and active sleepers while reducing the confined feeling often associated with traditional sleeping bag liners.

Integrated Armholes for Improved Comfort and Usability

Integrated armholes allow greater movement around camp and inside the sleeping bag without needing to fully exit the liner.

This improves comfort when reading, adjusting equipment or moving naturally during colder evenings and mornings.

HeiQ Fresh Odour Control for Extended Trip Freshness

HeiQ Fresh odour-control treatment helps reduce odour build-up during prolonged use between washes.

Combined with quick-drying fabric performance, this improves practicality during extended backpacking trips, hut stays and travel.

Features and Technologies

Significant Thermal Boost

The Reactor Midweight Liner is designed to increase sleeping warmth by up to 6°C / 11°F while remaining more lightweight and packable than carrying a substantially warmer sleeping bag.

This additional thermal performance helps extend the comfort range of your sleep system during colder nights and shoulder-season conditions.

Sleeping Bag Compatibility

The liner fits inside virtually all sleeping bags and can snap directly into compatible Sea to Summit sleeping bags for more secure positioning during sleep.

This helps reduce twisting and movement overnight while improving ease of entry and exit.

Protects Sleeping Bag Insulation

Using a liner helps reduce sweat, dirt and body oils reaching the sleeping bag insulation.

This reduces washing frequency and helps preserve insulation loft, warmth retention and long-term sleeping bag performance.

Fit and Size Guidance

Long Length Fit

The Long version is designed for users up to approximately 198 cm in height.

Its mummy-shaped profile improves thermal efficiency while the stretch-knit construction and integrated armholes maintain freedom of movement and sleeping comfort throughout the night.

Despite its increased warmth and longer dimensions, the liner remains compact enough for backpacking and travel use.

Features Summary

  • Thermolite Pro fleece insulation
  • FIR heat-reflective technology
  • Adds up to 6°C / 11°F warmth
  • Stretch-knit construction for unrestricted movement
  • Integrated armholes for comfort and usability
  • HeiQ Fresh odour-control treatment
  • Quick-drying performance
  • Compatible with Sea to Summit sleeping bags
  • Helps extend sleeping bag lifespan
  • Lightweight mummy-shaped construction
  • Includes Ultra-Sil stuff sack

Explore More Sleeping Bag Accessories

If you are building a more adaptable sleep system for backpacking, winter camping or travel, it may also be worth exploring our wider range of sleeping bag liners, sleeping mats and sleeping bags.

Midweight thermal liners like the Reactor Midweight series provide a practical way to increase warmth and sleeping comfort without needing to move to a significantly heavier cold-weather sleeping bag.

Technical Information
SpecificationDetails
Best useBackpacking, Camping & Winter Camping
ShapeMummy
Added warmthUp to 6°C
MaterialThermolite® Pro & Thermolite® EcoMade
Odour controlHeiQ Fresh
Maximum user height198cm
Weight355g
IncludesUltra-Sil stuff sack
CompatibilityFits all sleeping bags & compatible Sea to Summit snap systems
Sizing Information
Professional Opinion
Product Reviews
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