Tripbooks design system / lab 19 / the inter question

Lab 19 / one family instead of two

Inter against Archivo and Plex.

The question: replace the two text faces, Archivo for titles and IBM Plex Sans for language, with Inter carrying both, using its optical size axis so titles and body come from one family. Mono stays IBM Plex Mono in both treatments; a number is data and this lab does not touch it.

Readability under big content is the deciding factor, so every specimen below is real platform content at real platform sizes, and the dense register appears in full, twice. A · Archivo + Plex Sans  B · Inter, one family

01 / anatomy at the sizes we actually use

Where the readability difference physically comes from.

The blue rules sit at the same height in both columns. Inter's x-height is visibly taller at the same point size, which is the single biggest reason it reads more easily at 12.5px: more of every letter lives in the zone your eye scans.

A IBM Plex Sans · 12.5px body
marchetti group agreed
Free cancellation to 28 August, payable forty-five days before arrival. The airline holds the fare, not us, and nothing is guaranteed until tickets are issued. A key account since March 2023, quoting often and deciding slowly.
Illinois · Bill Illsley · Ill · Il1l · 11 Sep
THE I l 1 TEST · Plex's lowercase l carries a tail by default
B Inter · 12.5px body
marchetti group agreed
Free cancellation to 28 August, payable forty-five days before arrival. The airline holds the fare, not us, and nothing is guaranteed until tickets are issued. A key account since March 2023, quoting often and deciding slowly.
Illinois · Bill Illsley · Ill · Il1l · 11 Sep
THE I l 1 TEST · Inter's default l is a plain bar, capital I and l can collide
The title voice · 27px, the platform's page-title size
A Archivo · wdth 116 · wght 350
Marchetti Group
Sales analytics
Kyoto incentive, autumn board offsite
B Inter · opsz 32 · wght 460
Marchetti Group
Sales analytics
Kyoto incentive, autumn board offsite
What each column is quietly showing

At body size, B is the easier read: taller x-height, wider apertures on a e s c, and Inter's optical size axis serves a slightly sturdier cut at small sizes automatically. At title size, A has the identity: Archivo's width axis gives the platform its wide, engineered voice, and Inter at display size is deliberately neutral, closer to a very good system font. The trade is real in both directions, which is why the next two sections show whole screens instead of specimens.

02 / big content, the deciding case

The same register, in full, twice.

All Customers from Lab 05, identical data, identical widths, identical mono columns. Only the language face changes; scan for the customer names, which is the reading a person does two hundred times a day.

A  Archivo titles · Plex Sans language

Customers
ExportNew customer
CustomerTypeStatusTotal spendOutstandingEnquiry · quote · bookingLast bookingAgent
Sterling Capital GroupCCN-1001CorporateActive2,453,870386,720 57·53·4724 Jul 2026Sarah Mitchell
Meridian Health GroupCCN-1002SUPPCorporateActive1,920,0900 39·33·3122 Feb 2026James Carter
Marchetti GroupCCN-1055CorporateActive1,284,50076,300 18·14·1102 Aug 2026Sarah Mitchell
Aurora Travel PartnersACN-3001AgencyActive940,0750 23·18·1523 Sep 2025Emily Rodriguez
Mr. Jonathan PierceICN-2007IndividualActive803,46556,870 24·18·1412 Jul 2026James Carter
Globe OTA HoldingsACN-3009AgencyProspect58,9000 22·13·813 Jan 2026Sarah Mitchell
Brooks Travel CoACN-3006STOPAgencyActive22,400195 18·11·402 Apr 2025Nour Haddad
Vertex Trading FZECCN-1019CorporateProspectAED 25,700AED 17,160 3·3·112 Jun 2026Sarah Mitchell
8 of 43 shown7,508,700537,245204·165·131

B  Inter, one family for titles and language

Customers
ExportNew customer
CustomerTypeStatusTotal spendOutstandingEnquiry · quote · bookingLast bookingAgent
Sterling Capital GroupCCN-1001CorporateActive2,453,870386,720 57·53·4724 Jul 2026Sarah Mitchell
Meridian Health GroupCCN-1002SUPPCorporateActive1,920,0900 39·33·3122 Feb 2026James Carter
Marchetti GroupCCN-1055CorporateActive1,284,50076,300 18·14·1102 Aug 2026Sarah Mitchell
Aurora Travel PartnersACN-3001AgencyActive940,0750 23·18·1523 Sep 2025Emily Rodriguez
Mr. Jonathan PierceICN-2007IndividualActive803,46556,870 24·18·1412 Jul 2026James Carter
Globe OTA HoldingsACN-3009AgencyProspect58,9000 22·13·813 Jan 2026Sarah Mitchell
Brooks Travel CoACN-3006STOPAgencyActive22,400195 18·11·402 Apr 2025Nour Haddad
Vertex Trading FZECCN-1019CorporateProspectAED 25,700AED 17,160 3·3·112 Jun 2026Sarah Mitchell
8 of 43 shown7,508,700537,245204·165·131
What to look for, row by row

Names in B sit larger on the same 31px row without the row growing, because the extra size is x-height, not ascenders. Weight 500 in Inter reads a touch heavier than Plex's 500, so bold names separate from plain cells slightly more. The cost is width: Inter sets a little wider at the same size, so "Aurora Travel Partners" and the agent column consume a few more pixels each, which on a ten column register is the difference that eventually pushes a column into the scroll.

03 / the honest comparison

The booking header, one copy, live toggle.

Side by side comparisons let the eye cheat by comparing shapes instead of reading. The button at the bottom of the screen flips this one section in place, same pixels, which is how a real difference in reading comfort shows itself.

Marchetti Group
BKG-7QP2K4M9 RemindShare travel packIssue items
Issuing Partially paid MICE · 24 pax FROZEN v1.2
Customer
Marchetti Group
Agent
Sarah Mitchell
Travel
14 - 21 Sep 2026
Departs in
25 days
Total sell
$196,300.00
Due
$76,300.00
Coverage
$1,600.00 of headroom. The next item costs $18,900.00, so it needs a payment or a dual signed release before it can issue. The customer's balance is due 01 Sep; the cheapest rate option stops being refundable eleven days before you know whether they have paid.

04 / where the display face matters most

The customer document, side by side.

Titles do their real work on the customer side, where the document is the product. This is the one place Archivo's identity earns money, and the one place Inter's neutrality costs most, or reads most professional, depending on the eye. Yours decides.

A  Archivo
Quotation QUT-5RD9K3WP · version 1.2
Kyoto incentive, autumn board offsite
Accepting confirms this itinerary at these prices, on the terms above. You will be asked to sign electronically, and we will send confirmations as each part is secured.
TotalUSD 196,300.00
B  Inter
Quotation QUT-5RD9K3WP · version 1.2
Kyoto incentive, autumn board offsite
Accepting confirms this itinerary at these prices, on the terms above. You will be asked to sign electronically, and we will send confirmations as each part is secured.
TotalUSD 196,300.00

05 / the measurements, stated plainly

What each treatment actually buys.

FactorFinding
Body readability at 12.5pxInter wins, and it is the reason Inter exists: taller x-height, wider apertures, an optical size axis that serves a sturdier cut at small sizes automatically. On the register, names read a touch larger on the same 31px row.
The I l 1 problemPlex wins by default: its lowercase l carries a tail, Inter's is a plain bar. Matters in names and codes set in the language face; references and everything mono are unaffected because Plex Mono stays. Inter ships an alternate tailed l (cv05), but the Google Fonts build does not expose it reliably, so counting on it means self-hosting the font.
Width and densityInter sets slightly wider at equal size. A few pixels per cell across ten columns; the register still fits at 1280, but the margin that was spare becomes spent. Measurable in section 02 by comparing where each table's rows end.
Identity at title sizesArchivo wins. The wdth axis is the platform's voice, and it is what makes the customer document not look like every SaaS product of the decade, most of which set Inter. Inter at opsz 32 is excellent and anonymous.
One family instead of twoReal simplification: one font request instead of two, one vertical rhythm, no title-body pairing decisions ever again, and Inter's variable file covers 100 to 900 with the optical axis. The spec's three-face law becomes a two-face law: Inter for everything read, Plex Mono for everything counted.
Weight renderingInter's 500 reads slightly heavier than Plex's 500 on macOS antialiasing, which mildly improves name-versus-cell separation in tables; the existing 400/500/600 ladder maps across without retuning.
Cost to adoptTwo token values (--tb-display, --tb-sans), title settings change from wdth to opsz per role, and the lab bundle regenerates by script. Half a day including re-checking the register at 768 for the width creep. No structural change anywhere.

Ruled · 20 Aug 2026, after team consultation

Inter, unified. It is a verdict.

  1. Inter carries display and language platform-wide. Titles through the optical axis (opsz auto, weights 380 to 570), body at 12.5px where the register proved the readability gain. Archivo and IBM Plex Sans retire from the system.
  2. IBM Plex Mono is unchanged. A number is data; the two-face law replaces the three-face law.
  3. The I l 1 trade is accepted, with its fix recorded. The Google Fonts build does not reliably expose Inter's tailed lowercase l (cv05); the build note in the handbook says self-host Inter to enable it platform-wide, which closes the one legibility case Plex won.

Applied on ruling: the specification, handbook, every lab and the hosted site now render in Inter, and the tokens carry it. This page keeps all four families on purpose; it is the record of the comparison.